Q 1 – If the distance between the two objects is doubled, What will be the new gravitational force?
If the distance between two objects is doubled the gravitational force becomes one fourth since,
Where R is the diatnce between the bodies .
So , if R’ = 2R then
Q 2 – A particle is dropped from a tower 180 m high. How long does it take to reach the ground? What is its velocity when it touches the ground?
Given that,
Distance from which the ball is dropped, s = -180 m (negative sign for downward displacement)
Initial velocity, u = 0 m/s
Acceleration due to gravity, g = – 10 m/s
Using the second equation of motion,
Q 3 – The Earth and the Moon are attracted to each other by gravitational force. Does the Earth attract the Moon with a force that is greater or smaller or the same as the force with which the Moon attracts the Earth? Give appropriate reason to support your answer.
Let m and M be the mass of moon and earth respectively which are separated by a distance r
Force of attraction that earth exert on moon, Fe 
Thus earth attracts the moon with same force by which moon attracts the earth.
Also the gravitational force is an internal force of attraction between the two bodies, thus they have to be equal.
Q 4 – What is the magnitude of the gravitational force between the Earth and a 1kg object on its surface? (Mass of the Earth is 6×1024 kg and the radius of the Earth is 6.4×106 m).
Here, mass (m) of the body =1kg mass (Me) of the earth =6×1024kg, radius (Re) of the earth =6.4×106m Magnitude of the gravitional force between the earth and 1kg object.
Q 5 – A body is thrown up with a velocity of 40 m/s. How long does it take to reach the highest point? After how much time will the body come back to the ground? (g = 10 m/s2)
Here, u = 40m/s
V = 0 ( highest point)
A = g = -10m/s²
T = ?
By using,
V = u + at
0 = 40 + -10t
T = 4seconds
Time taken back to ground is
T = 4 +4 = 8seconds
Q 6 – A fruit falls from a tree takes 2 sec to reach the ground. Find its velocity on striking the ground.
Given, u = 0, t = 2 s, a = g = 9.8 m/s2, v = ?
From the first equation of motion,
v = u + at
= 0 + 9.8 × 2
= 19.6 m/s
Directions: In each of the following questions, a statement of Assertion is given and a corresponding statement of Reason is given just below it. Of the statements, given below, mark the correct answer as:
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both Assertion and Reason are false.
Q 7 – Assertion : Universal gravitational constant G is a scalar quantity.
Reason : The value of G is same throughout the universe.
a) Both assertion and reason are true and reason is the correct explanation of assertion.
Q 8 – Assertion : A man is sitting in a boat which floats on a pond. If the man drinks some water from the pond, the level of water in the pond will decrease.
Reason : The weight of the liquid displaced by the body is greater than the weight of the body.
(c) Assertion is true but reason is false.
Q 9 – Assertion : Any two objects in the universe attract each other by a force called gravitation force.
Reason : The force of gravitation exerted by the earth is called gravity.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
Q 10 – Assertion : Weight of a body on earth is equal to the force with which the body is attracted towards the earth.
Reason : Weight of a body is independent of the mass of the body.
(c) Assertion is true but reason is false.
Q 11 – Assertion : If we drop a stone and a sheet of paper from a balcony of first floor, then stone will reach the ground first.
Reason : The resistance due to air depends on velocity only.
. (c) Assertion is true but reason is false.
Q 12 – Assertion : It is the gravitational force exerted by the sun and the moon on the sea water that causes to the formation of tides in the sea.
Reason : Gravitational force of attraction is a strong force.
(c) Assertion is true but reason is false.
Q 13 – When an object is thrown vertically upward, on reaching the highest point, the value of acceleration due to gravity will be :
(a) 4.9 m/s2
(b) 9.8 m/s2 upwards
(c) 9.8 m/s2 towards the ground
(d) 0 m/s2
(c) 9.8 m/s2 towards the ground
Q 14 – Calculate the force of gravitation between the Earth and the Sun, given that the mass of the Earth is 6×1024 kg and of the Sun is 2×1030 kg. The average distance between the two is 1.5×1011 m.
Mass of earth m=6×1024 kg
Mass of Sun M=2×1030 kg
Distance between sun and earth r = 1.5 × 1011 m
Force of gravitation between them 
Q 15 – A bus and a car moving with equal velocity. On applying brakes, both will stop after certain distance. Then :
(a) Bus will cover less distance before coming to rest
(b) Car will cover less distance before coming to rest
(c) Both will cover equal distances
(d) None of the above
(b) Car will cover less distance before coming to rest
Q 16 – The mass of the body on moon is 40 kg, what is the weight on the earth.
(a) 240 kg (b) 392 N
(c) 240 N (d) 400 kg
. (b) 392 N
Q 17 – A body weighs 5 kg in air and 3 kg when fully immersed in water.
- Find the apparent loss in weight of the body.
- The upward thrust on the body.
- The volume of the body. (take g = 10 m/s2)
Given, Mass of the body in the air,
ma = 5 kg
Mass of body when immersed in water,
mw = 3 kg
1. The apparent loss in weight = weight of the body in air – weight of the body in water
= 50 N – 30 N = 20 N
Apparent loss in weight = 20 N
2. Upthrust on the body = loss in weight of the body = 20 N
3. The volume of the body = volume of liquid displaced
Q 18 – Obtain a relation between the weight of an object on the surface of Earth and that on Moon.
Weight of an Object on the Surface of Moon
Since, mass of the moon is less than that of earth, therefore, moon will exert less force of attraction on any object; in comparison to the earth. Acceleration due to gravity on moon is ‘gm’. Or, Weight of an object on the moon = 1/6th of the weight of the object on earth.
Q 19 – Show that the weight of an object on the moon is 1/6 th of its weight on the earth.
Suppose the mass of the moon is Mm and its radius is Rm. If a body of mass m is placed on the surface of the moon, then the weight of the body on the moon is
Weight of the same body on the earth’s surface will be
where Me = mass of earth and Re = radius of earth.
Dividing equation (1) by (2), we get
Now, mass of the earth, Me = 6 × 1024 kg
mass of the moon, Mm = 7.4 × 1022 kg
radius of the earth, Re = 6400 km
and radius of the moon, Rm = 1740 km
Thus, equation (3) becomes,
The weight of the body on the moon is about one-sixth of its weight on the earth.
Q 20 – On the moon’s surface, the acceleration due to gravity is 1.67 ms-2. If the radius of the moon is 1.74 × 106 m, calculate the mass of the moon.
(G = 6.67 × 1011 Nm2kg-2)
Here, g = 1.67 ms-2, R = 1.74 × 106 m and G = 6.67 × 10-2 Nm2 kg-2
Q 21 – From a cliff of 49 m high, a man drops a stone. One second later, he throws another stone. They both hit the ground at the same time. Find out the speed with which he threw the second stone.
For the first stone
u = 0 ms-1, h = 49 m,
i.e., the First stone would take 3.16 s to reach the ground.
For the second stone,
the time taken by the second stone to reach the ground is one second less than that taken by the first stone as both stones reach the ground at the same time.
That is, for the second stone, t = (3.16 – 1)s = 2.16s
∴ For the second stone,
g = 9.8 ms-2, h = 49 m, t = 2.16 s, u = ?
i.e., the second stone was thrown downward with a speed of 12.1 ms-1.