Conservation of Energy

Question

Shadow · Answer

4. A 0.005 kg nickel hits the ground with a kinetic energy of 1519 J
a. From what height was it dropped?
b. What was its velocity when it hit the ground?

Shadow · Answer

Solved for a, it is 31,000

Angle · Answer

31000 meters?

Shadow · Answer

yes

Angle · Answer

let's use the kinematic equation
$(v_f)^2 = (v_i)^2 + 2ad$

where vf is what we are looking for
starting velocity is 0
acceleration is 9.8
distance is 31000 meters

Shadow · Answer

So we need kinematics for this?

So far the equations we use for these situations are:

PE = mgh
KE = (1/2)mv^2

Where PE = Potential energy, KE = Kinetic energy

Angle · Answer

here's the example I found https://www.quora.com/If-a-mass-of-4-kg-is-dropped-from-a-height-of-100-meters-what-is-its-velocity-when-it-touches-the-ground

Shadow · Answer

Okay let me look at it

Shadow · Answer

Okay I got the same thing with KE and PE formulas which comes out to 779.5m/s

But the answer sheet has it as negative. No idea why.

Shadow · Answer

Cant square a negative, so I assume it is just "object is going towards Earth therefore we make the velocity negative" and this is all just a direction thing.

Shadow · Answer

Thank you for the link though, it helped reaffirm that I was not doing something wrong with my math and setup xD