A pebble is dropped freely in a well from it's top. It takes 20 s for the pebble to reach the water surface in the well. Taking g = 10 m s^-2 and speed of sound = 330 m s^-1, find: (i) the depth of water surface, and (ii) the time when echo is heard after the pebble is dropped.

A ball is thrown vertically upwards from the top of a tower with an initial velocity of 19.6 m s^-1. The ball reaches the ground after 5 s. Calculate: (i) the height of the tower, (ii) the velocity of ball on reaching the ground. Take g = 9.8 m s^-2

Assertion (A) : Inertia is an inherent property of each body by virtue of which it has a tendency to resist the change in its state of rest only.

Reason (R) : Force is that external cause which tends to change the state of rest or the state of motion of an object.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Assertion (A) : A cricket ball acquires much smaller velocity than a tennis ball when the two balls are pushed with equal force for the same duration.

Reason (R) : Mass is a measure of inertia.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false