Justina and Shauna throw identical stones from the top a tall building. Justina

Question

Justina and Shauna throw identical stones from the top a tall building. Justina throws her stone upward, while Shauna throws hers downward. If both stones were thrown with the same initial speeds, then which of the following are true?

A) Justina’s stone will land with a greater impact velocity.

B) Shauna’s stone will land with a greater impact velocity.

C) Both stones will land with the same impact velocity.

D) Justina’s stone will land with more kinetic energy.

E) Shauna’s stone will land with more kinetic energy.

Explanation / Answer

In this case we have that Justina threw her stone upwards with a certain initial speed. When an object is thrown up with a certain speed it will slow down over time because gravity, which is an acceleration, is pulling down (the opposite direction of the throw) therefore, have a negative sign which mean is decelerating the object until the speed reaches zero then the only force that it have is, again, gravity that now is not decelerating the object but accelerating it downwards starting with an initial velocity of zero and since is accelerating going down at the same ratio that he was decelerating while going up then the object will take the same ammount of time going back to starting point than it took to go at the maximum point, so, it will regain the initial velocity it had when it was thrown by the time it reaches the initial launch point.

All of this means that Justina will see the stone coming down at the same speed she threw it up so it will be just like Shauna's stone just a bit late (because Justina's had to go up and then down) but they both will go down at the same speed from the same point (but at different times)

If we see the answers we have that the impact velocity of one or the other is higher or the same and the answer is that Both stones will land with the same impact velocity since both had the same initial velocity and will cover the same distance.

Other answers we could chose are about the kinetic energy but kinetic energy is based on mass and velocity and since the 2 stones had same mass and where thrown with same velocity means that they both had the same Kinetic energy so neither D or E are good answers.

So final answer is C

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