NEETPhysicsMotion in One Dimension
A rubber ball is dropped from a height h onto a hard floor. It hits the floor and bounces back perfectly elastically to the same height. Taking the downward direction as positive, which of the following correctly describes the velocity-time ( v-t ) graph for the motion of the ball from the moment it is dropped until it reaches its maximum height again?
Options
- ATwo parallel straight line segments with the same positive slope, separated by a sudden jump from a positive t
- BA continuous V-shaped graph entirely above the time axis, starting from the origin.
- CA continuous zig-zag graph with alternating positive and negative slopes, starting from the origin.
- DA single continuous straight line starting from a negative velocity, crossing the time axis to a positive velo
Correct answer
A. Two parallel straight line segments with the same positive slope, separated by a sudden jump from a positive t
Step-by-step solution
Let the downward direction be positive. The ball is dropped, so its initial velocity is zero. During the downward fall, the acceleration is a = +g (constant). The velocity increases linearly according to v = gt . This is represented by a straight line starting from the origin with a positive slope. Upon perfectly elastic impact with the floor, the velocity of the ball instantly reverses its direction but maintains its magnitude. Thus, the velocity abruptly changes from a positive value ( +v₀ ) to a negative value (