Q 3.19 Suggest a suitable physical situation for each of the following graphs.
(a)The particle is initially at rest. Then it starts moving with a constant velocity for some time and then its velocity changes instantaneously and it starts moving in the opposite direction, crosses the point where it was at rest initially and then comes to a halt.
A similar physical situation arises when a bowler throws a ball towards the batsman, the ball travels towards the batsman with some constant speed and after the batsman hits it the ball goes past the bowler and gets caught by a fielder and its velocity comes down to zero within an instant.
(b)The velocity of a particle starts coming down to zero from some velocity with some constant acceleration, goes to zero and changes its direction. Then suddenly the direction of velocity changes and magnitude decreases.
This is the case when a ball is thrown in the air. It starts moving with some velocity and gets retarded by g, its velocity becomes zero at the highest point and its velocity then changes direction and as it hits the ground it loses some of its speed and gets rebound and this keeps on happening till it comes to rest.
(c) The acceleration of a body is zero. It increases to some value for a very small period of time and again comes to zero.
This is the case when a football travelling horizontally hits a wall or gets kicked by a player.