Free Fall Problem: Calculating Projectile Motion from a Cliff Edge

[shawonna23]

Help! Free Fall Problem

A pellet gun is fired straight downward from the edge of a cliff that is 13 m above the ground. The pellet strikes the ground with a speed of 30 m/s. How far above the cliff edge would the pellet have gone had the pellet been fired straight upward?

 

[Tide]

What have you done so far?

 

[shawonna23]

I started using the equation :

y=-1/2 gt^2-30t+0

 

[veryyoung]

are you assuming that 30 m/s is not the pellets terminal velocity?

 

[Tide]

Have you learned about energy conservation yet? If so then you can use it to find what the "muzzle velocity" is. Basically it says that $\frac{1}{2}mv^2_{final} - mg \times 30 = \frac{1}{2}mv^2_{initial}$, i.e. potential + kinetic energy is constant.

 

[shawonna23]

yes, I'm assuming that 30m/s is not the pellets terminal velocity

 

[pervect]

I started using the equation :

y=-1/2 gt^2-30t+0

Hmmm, that's not the right equation - did you understand the remarks Tide made about energy conservation?