Question

Suppose a ball of mass $m$ is thrown vertically upward with an initial speed $v$; its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fall downward and attains the speed $v$ again before striking the ground. It implies that the magnitudes of initial and final momenta of the ball are same. This is an example of:

• A. conservation of momentum
• B. conservation of energy
• C. conservation of speed
• D. none of these

Answer 1

Answer: (B)

conservation of energy

The sum of energy is always constant in any of the positions of the ball.
The momentum magnitude remained same but the direction is reversed in the above case as the velocity of the ball is reversed, initially moving up and then going down , it was possible as only conservative forces ( gravity force) were acting on the object, hence the total energy of system was conserved .