# Collisions: Ball with initial velocity is kicked, force of kick?

1. Nov 26, 2011

### Merlinnair

1. The problem statement, all variables and given/known data
A 10 g ball going at a speed of 5 m/s is kicked, and flies off at an angle of 35° at 25 m/s. What was the force of kick?
Known:
m = 0.0010 kg
vi = 5 m/s
θ = 35°
vf = 25 m/s

2. Relevant equations
mvi = mvf
F = ma

3. The attempt at a solution
Would this count as an inelastic collision?
In the x direction:
.0010g(5m/s) + m(0m/s) = (.0010 kg + m)(25cos35)

After that, I'm really not sure how to get to the acceleration...

2. Nov 26, 2011

### Staff: Mentor

This is an impulse-momentum problem, not a momentum conservation problem. (You'll need the time during which the kick was applied.)

3. Nov 27, 2011

### Merlinnair

In that case, I might have forgotten a variable, as I don't have the question with me. So if I had the time...

Impulse is F/t and change in momentum right?

So then, all I'd have to do is set F/t = p_i - p_f?

4. Nov 27, 2011

### Staff: Mentor

Almost. Impulse is F*t, not F/t.
Set impulse = Δp. (FYI: Change in something is always final - initial.)

5. Nov 27, 2011

### Merlinnair

Oh, right, typo on the change in part, and I really do need to start memorizing my equations. Thanks for your help!