Q5 of 14 Page 16

Give scientific reasons.

When an object falls freely to the ground, its acceleration is uniform.

If we neglect air drag then no other force was applied except Gravitational Force.

We know, Gravitational Force


Where m1 is the mass of the object & m2 is the mass of the earth.


Or we can write as,



for free falling body, Gm2=constant, so



So, logically acceleration keeps increasing during free fall. No, the acceleration due to gravity is not uniform


But, in real life the increase of acceleration is negligible because here,


d= R + r + x


where R= radius of earth=6400 km (approx),


r =radius of falling body,


x=distance of surface.


So d is almost equal to R for almost every practical case, hence we assume g=constant. Thus near the surface, acceleration due to gravity is taken to be uniform.


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3

Complete the following table.

 4

Complete the sentences and explain them.

A. The minimum distance between the start and finish points of the motion of an object is called the ______ of the object.


B. Deceleration is ______ acceleration


C. When an object is in uniform circular motion, its ______changes at every point.


D. During collision ______remains constant.


E. The working of a rocket depends on Newton’s ______ law of motion.

 5

Give scientific reasons.

Even though the magnitudes of action force and reaction force are equal and their directions are opposite, their effects do not get cancelled.

 5

Give scientific reasons.

It is easier to stop a tennis ball as compared to a cricket ball, when both are travelling with the same velocity.