Question

Two objects are thrown from the top of a tall building and experience no appreciable air resistance. One is thrown up, and the other is thrown down, both with the same initial speed. What are their speeds when they hit the street?A. The one thrown up is traveling faster.B. The one thrown down is traveling faster.C. They are traveling at the same speed.

Answer 1

Answer:

C. They are traveling at the same speed.

Explanation:

Lets  take height of the building = h m

The mass of the objects = m kg

Initial velocity = u m/s

When objects thrown upward :

By using energy conservation

Work done by all the forces =Change in the kinetic energy of the objects

$m g (-y) + m g ( h + y) = \dfrac{1}{2}mv^2- \dfrac{1}{2}mu^2$

$mgh= \dfrac{1}{2}v^2- \dfrac{1}{2}u^2$

$v=\sqrt{2gh+u^2}}\ m/s$

When objects thrown downward :

By using energy conservation

Work done by all the forces =Change in the kinetic energy of the objects

$mg h= \dfrac{1}{2}mv^2- \dfrac{1}{2}mu^2$

$mgh = \dfrac{1}{2}v^2- \dfrac{1}{2}u^2$

$v=\sqrt{2gh+u^2}}\ m/s$

We can say that both the objects are having same velocity when they hit the ground.

Therefore the answer will be C.