# Physics Potential/kinetic energy question.?

Hi all,

So here is the question:

The spring constant (K) of a toy dart gun is 5000N/M. To **** the gun the spring is compressed by 0.03m. The 0.007Kg dart is fired straight up and reaches a max height of 24m.

a) Determine the energy dissipated by air friction during the trip upward.

b) Assuming the same energy dissipation during the trip downward, estimate the speed of the dart when it returns to the starting point.

I'm guessing that I have to split this problem into 3 sections of motion....but I have no idea where to begin, I would appreciate it very much if anyone could lend a help.

Thank you all for the generous help.

I dont know why they censor C 0 c. K.......**** = C.0c ..K the gun...meaning loading the dart....

### 1 Answer

- PeterLv 46 years agoFavorite Answer
If the air is gone, the potential energy from the spring should equal the potential energy the dart has when it reaches maximum height, but that's not the case here. The potential energy from the spring = force x dist. (spring compression) x (distance spring goes back to original length) = work of spring x distance = 1/2 k X2. The difference between that and the potential energy the dart has at its height (mgh) equals the energy lost to the air.

To figure the darts velocity on the way down the the potential energy - what is lost to the air is converted to kinetic energy (1/2 m v2).