Question

A bullet with a mass of 12.0g traveling toward the right at 260m/s strikes a large bag of sand and penetrates it to a depth of 23cm. Determine the magnitude and direction of the friction force (assumed constant) that acts on the bullet. PLEASE HELP!

Answer 1

Using work and kinetic energy theorem:
\[W=K'-K \\ f\Delta x=0-\frac12mv^2 \\ f=-\frac{mv^2}{2\Delta x } \] f is in left direction in the pic.

Answer 2

I'm sorry I should have said something but can it be solved using the laws of motion? We have not been taught the energy theorems yet. I know they will both work but I'm having problems figuring this out.

Answer 3

Yes, it can be solved in many ways. The bullet move with constant acceleration of \(f/m\).
You can use kinematics then.

Answer 4

I used \[V^2=V^2+2a \Delta x \]

to solve for acceleration and then used f=ma for the force

Answer 5

ok then for the vertical I used Fn-mg=ma where ma=0, making Fn=mg.

Answer 6

There isn't any forces acting upward on the projectile right?

Answer 7

Actually, you don't need to consider vertical motion or vertical force acting on object. It already covered by the word "constant friction".

Answer 8

Awesome thanks a ton! I think I can handle it from here.

Answer 9

Okay :)