Class 10 Science SEE Guide | Unit - 7 Motion and Force Guide 2080

Class 10 Science SEE Guide

Unit - 7

Motion and Force Guide

Exercise

1. Choose the correct option for the following questions:

(b) What is the change in the gravitational force between two objects when their mass is doubled?

(i) The force doubles

(ii) the force becomes four-time

(iii) the force is reduced two times

(iv) The force is decreased four times

Answer 👉 (ii) the force becomes four-time

(c) The gravitational force between two objects on Earth is 60 N, what is the gravitational force between those two objects on the moon?

(i) 10N

(ii) 6N

(iii) 9.8 N

(iv) 60 N

Answer 👉 (ii) 6N

(d) Which one of the following statements is correct?

(i) The value of acceleration due to gravity increases as we go deeper from the surface of the earth.

(ii) The value of acceleration due to gravity decreases as the height above the surface of the earth increases.

(iii) The value of acceleration due to gravity is less in the - polar region than that in the equatorial region.

(iv) The value of the acceleration of gravity is highest at the highest place on the Earth.

Answer 👉 (ii) The value of acceleration due to gravity decreases as the height above the surface of the earth increases.

(e) At which of the following places do you weigh the most?

(i) peak of Mount Everest

(ii) peak of Api Himal

(iii) Kechnakwal of JThapa

(iv) Chandragiri Hills

Answer 👉 (i) peak of Mount Everest

(f) The radius of the Earth is 6371 km and the weight of an object on the earth is 800 N. What is the weight of the object at a height of 6371 km from the surface of the earth?

(i) B0ON

(ii) 1600 N

(iii) 200 N

(iv) 3200 N

Answer 👉 (iii) 200 N

(g) If the mass and the radius of a celestial body are two times the mass and the radius of the earth respectively, what is the value of acceleration due to the gravity of that body?

(i) 9.8 ms*

(ii) 4.9ms*

(iii) 19.6ms™

(iv) 10ms™

Answer 👉 (iii) 19.6ms™

(h) What will be the weight of a man on the moon, if his weight on earth is 750 N? (The acceleration due to the gravity of the moon = 1.63 m/s?)

(i) 124.74N

(ii) 125 N

(iii) 126.8 N

(iv) 127.8 N

Answer 👉 (ii) 125 N

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2. Differentiate between:

(a) Gravitational constant G and acceleration due to gravity g

Answer 👉

Gravitational constant G: It is a constant value denoted by G and is a fundamental constant in physics. It represents the strength of the gravitational force between two objects. Its value is approximately 6.674 × 10^-11 N(m/kg)^2.
Acceleration due to gravity g: It is the acceleration experienced by an object when it is in the gravitational field of another object. It depends on the mass of the object creating the gravitational field and the distance from the object's center. On Earth's surface, the average value of acceleration due to gravity is approximately 9.8 m/s².

(b) Mass and Weight

Answer 👉

Mass: Mass is a measure of the amount of matter in an object. It is a scalar quantity and is measured in kilograms (kg). Mass remains constant regardless of the location of the object in the universe.
Weight: Weight is the force exerted on an object due to gravity. It is a vector quantity and is measured in newtons (N). Weight depends on the mass of the object and the acceleration due to gravity. The weight of an object can vary depending on the strength of the gravitational field.

3. Give reason:

(a) Acceleration due to gravity is not the same in all parts of the earth.

Answer 👉 Acceleration due to gravity is not the same in all parts of the earth because it depends on the distance from the center of the earth. The acceleration due to gravity decreases as we move farther away from the center of the earth, resulting in slight variations in different locations.

(b) Jumping from a significant height may cause more injury.

Answer 👉 Jumping from a significant height may cause more injury because the velocity gained during the fall increases with height. The greater the velocity upon impact, the higher the potential for injury due to the increased force exerted on the body.

(c) Mass of Jupiter is about 319 times themass of the Earth, but its acceleration due to gravity is only about 2.6 times the acceleration due to gravity of the Earth.

Answer 👉 The acceleration due to gravity is not solely dependent on the mass of an object but also on its radius. While the mass of Jupiter is much larger than that of the Earth, its larger radius results in a greater distance between its center and the surface, causing a relatively lower acceleration due to gravity compared to Earth.

(d) Among the objects dropped from the same height in the polar region and the equatorial region of the earth, the object dropped in the polar region falls faster.

Answer 👉 The object dropped in the polar region falls faster compared to the object dropped in the equatorial region because the polar region is closer to the Earth's axis of rotation. The centripetal force generated by the rotation of the Earth is slightly smaller at the poles, resulting in a slightly higher effective acceleration due to gravity and faster-falling speed.

(e) Out of two paper sheets, one is folded to form a ball. If the paper ball and the sheet of paper are dropped simultaneously in the air, the folded paper will fall faster.

Answer 👉 The folded paper will fall faster than the sheet of paper because the folded paper has a higher air resistance or drag coefficient. The irregular shape of the folded paper ball creates more air resistance, slowing down its descent less compared to the sheet of paper.

(f) When a marble and a feather are dropped simultaneously in a vacuum, they reach the ground together (at the same time).

Answer 👉 In a vacuum, both the marble and the feather experience the same acceleration due to gravity since air resistance is eliminated. Without air resistance, they fall at the same rate and reach the ground together.

(g) As you climb Mount Everest, the weight of the goods that you carry decreases.

Answer 👉 As you climb Mount Everest, the weight of the goods that you carry decreases because the acceleration due to gravity decreases with increasing distance from the center of the Earth. The decrease in gravitational force results in a decrease in the effective weight of the objects being carried.

(h) It is difficult to lift a big stone on the surface of the earth, but it is easy to lift a smaller one.

Answer 👉 It is difficult to lift a big stone on the surface of the Earth compared to a smaller one because weight is directly proportional to mass. The larger stone has a greater mass, leading to a higher gravitational force acting on it. This increased gravitational force makes it more challenging to overcome and lift the larger stone.

(i) Mass of an object remains constant but its weight varies from place to place.

Answer 👉 The mass of an object remains constant, but its weight varies from place to place because weight is the force exerted on an object due to gravity. Gravity varies depending on the location and altitude. The weight of an object is directly proportional to the gravitational force acting on it. Therefore, as the gravitational acceleration differs in various locations, the weight of an object will also change accordingly.

(i) One will have an eerie feeling when he/she moves down while playing a Rote Ping.

Answer 👉 One will have an eerie feeling when moving downward while playing on a rotating swing (Rote Ping) due to the sensation of centrifugal force. When the swing rotates, the person on the swing experiences an outward force, known as centrifugal force, that acts opposite to the direction of gravity. This centrifugal force creates a sensation of weightlessness or reduced weight, leading to the eerie feeling as the person moves downward against the upward centrifugal force. This contrasting force sensations can cause a disorienting and unsettling feeling.

4. Answer the following questions:

(a) What is gravity?

Answer 👉 Gravity is a fundamental force of nature that attracts objects with mass towards each other. It is responsible for the phenomenon of weight and the motion of celestial bodies.

(b) State Newton's universal law of gravitation.

Answer 👉 Newton's universal law of gravitation states that every particle in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Mathematically, it can be represented as F = G * (m1 * m2) / r^2, where F is the gravitational force, G is the gravitational constant, m1 and m2 are the masses of the two objects, and r is the distance between their centers of mass.

(c) Write the nature of gravitational force.

Answer 👉 The nature of gravitational force is attractive, meaning it pulls objects towards each other. It acts along the line joining the centers of mass of the two objects and is always attractive, regardless of the masses involved.

(d) Define gravitational constant (G).

Answer 👉 Gravitational constant (G) is a fundamental constant in physics that appears in the equation for Newton's law of universal gravitation. It represents the proportionality factor between the masses of two objects, the distance between them, and the strength of the gravitational force. Its approximate value is 6.67430 x 10^-11 N(m/kg)^2.

(e) Under what conditions is the value of gravitational force equal to the gravitational constant (F=G)?

Answer 👉 The value of gravitational force is equal to the gravitational constant (F = G) when the masses of the two objects are both equal to 1 kg and the distance between them is 1 meter. In this scenario, the gravitational force between the two objects would be equal to the value of the gravitational constant.

(f) Write two effects of gravitational force.

Answer 👉 Two effects of gravitational force are:

Weight: Gravitational force gives objects their weight. It is responsible for the force experienced by an object due to the gravitational attraction between the object and the planet or celestial body it is on. Weight is the force with which an object is pulled towards the center of the Earth or another massive body.

Orbital Motion: Gravitational force is responsible for the motion of celestial bodies in the universe. It keeps planets in orbit around the Sun, satellites in orbit around the Earth, and galaxies bound together. The gravitational force acts as a centripetal force, keeping objects in stable orbits.

(g) Mathematically present the difference in the gravitational force between two objects when the mass of each is made double and the distance between them is made one forth their initial distance.

Answer 👉 Mathematically, the difference in the gravitational force (F) between two objects when their masses are doubled (2m) and the distance between them is made one-fourth (r/4) of their initial distance (r) can be represented as follows:

Initial gravitational force: F1 = G * (m * m) / r^2

New gravitational force: F2 = G * ((2m) * (2m)) / (r/4)^2

Simplifying the equation:

F2 = G * (4m^2) / (r^2/16)

F2 = 16 * (G * m^2) / (r^2)

F2 = 16 * F1

Therefore, the new gravitational force (F2) is 16 times greater than the initial gravitational force (F1).

(h) What is gravitational force?

Answer 👉 Gravitational force is the force of attraction that exists between two objects with mass. It is responsible for the phenomenon of weight and is the force that keeps objects grounded on the Earth.

(i) Define acceleration due to gravity.

Answer 👉 Acceleration due to gravity is the acceleration experienced by an object when it is subjected to the gravitational force. It is the rate at which the velocity of an object changes under the influence of gravity. On the surface of the Earth, the average acceleration due to gravity is approximately 9.8 m/s².

(j) What is free fall? Give two examples of it.

Answer 👉 Free fall is the motion of an object under the sole influence of gravity, with no other forces acting upon it except for air resistance. Two examples of free fall are a skydiver falling through the atmosphere before opening their parachute and a dropped object falling towards the ground.

(k) Under what conditions is an object said to be in free fall?

Answer 👉 An object is said to be in free fall when it is only influenced by gravity and no other forces, such as air resistance or external forces, are acting upon it. In free fall, the object experiences acceleration due to gravity and follows a parabolic trajectory.

(l) Write the conclusions of the feather and coin experiment.

Answer 👉 The conclusions of the feather and coin experiment, conducted in a vacuum, are that both the feather and the coin fall with the same acceleration due to gravity and reach the ground simultaneously. This demonstrates that in the absence of air resistance, objects of different masses fall at the same rate.

(m) What is weightlessness?

Answer 👉 Weightlessness refers to the condition experienced by objects or individuals when they appear to have no weight or experience a loss of weight. It occurs in situations where gravitational forces are greatly reduced or canceled out, such as during free fall or in orbit around a celestial body.

(n) ‘Mention any four effects of gravitational forces,

Answer 👉 Four effects of gravitational forces are:

Weight: Gravitational forces determine the weight of objects and give rise to the force of gravity, which pulls objects towards the center of the Earth.
Orbital Motion: Gravitational forces are responsible for the motion of celestial bodies in orbits, such as planets revolving around the Sun or satellites orbiting the Earth.
Tides: Gravitational forces between the Earth, Moon, and Sun cause the phenomenon of tides in oceans and other bodies of water.
Gravitational Lensing: Gravitational forces can bend the path of light, causing the phenomenon known as gravitational lensing, which is used to study distant galaxies and other astronomical objects.

(p) Mention the factors that influence acceleration due to gravity.

Answer 👉 Factors that influence acceleration due to gravity include the mass of the celestial body (such as Earth or Moon) generating the gravitational field and the distance from the center of that body. The acceleration due to gravity decreases with increasing distance from the center of the body and increases with increasing mass of the body.

(q) The acceleration due to the gravity in the Earth surface is 9.8 m/s2. What does this mean?

Answer 👉 The acceleration due to gravity on the Earth's surface being 9.8 m/s² means that every second, an object near the Earth's surface experiences an increase in velocity by 9.8 meters per second due to the force of gravity.

(r) Mass of the Moon is about 1/81 times the mass of the Earth and its radius is about 37/10 times the radius of the Earth. If the earth is squeezed to the size of the moon, what will be the effect on its acceleration due to gravity? Explain with the help of mathematical calculation.

Answer 👉 If the Earth is squeezed to the size of the Moon while maintaining its mass, the effect on its acceleration due to gravity would be an increase. This is because the radius of the Moon is smaller than the radius of the Earth, and according to the equation for acceleration due to gravity, a decrease in radius leads to an increase in acceleration.

(s) The acceleration due to gravity of an object of mass 1 kg in outer space is 2m/s?. What is the acceleration due to the gravity of another object of mass 10 kg at the same point? Justify with arguments.

Answer 👉 The acceleration due to gravity is the same for objects of different masses at the same point. In this case, the acceleration due to gravity would be 2 m/s² for both the 1 kg object and the 10 kg object, as it is determined by the gravitational field at that specific location.

(t) A man first measures the mass and weight of an object in the mountain and then in the Terai. Compare the data that he obtains.

Answer 👉 When measuring the mass and weight of an object in the mountain and Terai regions, the mass of the object will remain the same in both places. However, the weight of the object will vary since weight depends on the acceleration due to gravity, which can be slightly different at different locations on Earth.

(u) A student suggests a trick for gaining profit in a business. He suggests buying oranges from the mountain selling them to Terai at the cost price.If a beam balance is used during this transaction, explain, based on scientific fact, whether his trick goes wrong or right.

Answer 👉 The trick suggested by the student to buy oranges from the mountain and sell them in Terai at the cost price will go wrong when using a beam balance. This is because the weight measured on the beam balance would be different in the mountain and Terai due to the variation in the acceleration due to gravity. Thus, the trick would not result in equal profit.

(v) How is it possible to have a safe landing while jumping from a flying airplane using a parachute? Is it possible to have a safe landing on the moon in the same way?Explain with reasons.

Answer 👉 It is possible to have a safe landing while jumping from a flying airplane using a parachute because the parachute increases air resistance, which counteracts the force of gravity and slows down the descent, allowing for a gentle landing. However, on the moon, there is no atmosphere to provide air resistance, so a parachute alone would not work for a safe landing.

(w) The acceleration of an object moving on the earth is in- versely proportional to the mass of the object, but for an object falling towards the surface of the earth, the accel- eration does not depend on the mass of the object, why?

Answer 👉 The acceleration of an object moving on Earth is inversely proportional to the mass of the object, but for an object falling towards the surface of the Earth, the acceleration does not depend on the mass of the object. This is because, in free fall, the gravitational force and the resulting acceleration due to gravity act on all objects equally, regardless of their mass. In this scenario, the mass cancels out in the equation, resulting in the same acceleration for all objects.