# Force exerted by a ball to

## Homework Statement

A barefoot field-goal kicker imparts a speed
of 37 m/s to a football initially at rest.
If the football has a mass of 0.41 kg and the
time of contact with the ball is 0.012 s, what
is the force exerted by the ball on the kicker’s
foot?

F=ma

## The Attempt at a Solution

F= .41 * (37/.012) = 1264.166667 N
Answer was wrong, wouldn't this obey newtons third law?

hage567
Homework Helper
You need to think of impulse and momentum for this problem.

so would it be,
impulse = force x time
1264.16667 N / .012 s = ans?

no... why are u trying to solve for impulse when you have to determine force? what are your known and unknown variables? define them... Delta t = 0.012s, massball = .... and so on

after defining your variables see if you are famliar with the impulse momentum formula:

mvf - mvi = momentum (where vf = final velocity and vi = initial velocity)
impluse = Force*delta t

impulse = momentum... maybe you can go about solving from there

Following your advice and retrying everything I still come up with the same answer that the Force = m ΔV/t

hmmm. the answer sounds correct. who told you that the answer was wrong? maybe the answer is supposed to have a negative sign???

hage567
Homework Helper
hmmm. the answer sounds correct. who told you that the answer was wrong? maybe the answer is supposed to have a negative sign???

I get the same answer as the OP. I agree that a negative sign may be needed, since it is equal and opposite to the force of the foot on the ball for Newton's third law.

It was just the negative sign! Thanks guys I was killing myself over this

how did u solve for it?? anyone?? i have the same problem?

Hey i just got it finally, the 37 is added to the 51.5 not subtracted due to it being in the opposite direction. The correct answer is 3750.