# Force Problem with football punter

[SOLVED] Force Problem

## Homework Statement

2. A football punter accelerates a football from rest to a speed of 10m/s during the time in which his toe is in contact with the ball (about 0.20sec). If the football has a mass of 0.50kg, what average force does the punter exert on the ball?

## Homework Equations

so far i have this and can't seem to find the equation(s) but i got some and does not correspond with the correct answer.

a=10ms/^2
t=.20sec
m=.50kg
F= thats what we need for answer

so F=ma

## The Attempt at a Solution

but i dont understand how we put our time in an equation to solve for Force, I know im missing something but i don't know what. I have the answer, answer only which does not help at all :P. Thats to check whether we get the correct problem

F = ma
F = 10m/s (.50kg)
F = 5N (?) but answer that was given was 25 N

I want to know how to do it :P even thou teacher gives us answer for homework. Which is the most important thing
I'm stuck with this help

Thank you in advance

## Answers and Replies

Astronuc
Staff Emeritus
Science Advisor
F = 10m/s (.50kg) is velocity * mass or mv which is the final momentum.

F = dp/dt or m dv/dt so take mass * (change in v)/(change in time)

a = dv/dt

F = 10m/s (.50kg) is velocity * mass or mv which is the final momentum.

F = dp/dt or m dv/dt so take mass * (change in v)/(change in time)

a = dv/dt

so F=ma:

F= 10ms/(.50kg) = 5 m/s correct which equals Velocity(?)

so for F= dp/dt what is dp? change in P(?) / change in time so we get

F= 5ms/.20s = 25N

my question comes from F=dp/dt we use that equation to find out Force? Where can we say that F=dp/dt (as u used) comes from?

srry if i sound confusing

Astronuc
Staff Emeritus
Science Advisor
p = m v = momentum.

Now let's take the case for constant mass.

F = dp/dt = d (mv) /dt = m dv/dt = m a

Back the problem.

m = 0.5 kg, which is accelerated from rest (v=0) such that at the end of 0.2 s, the mass has a velocity 10 m/s. So the change in velocity (dv) = 10 m/s - 0 m/s, and the change it time (or time interval), dt = 0.2 s.

so F = ma = m dv/dt

m = 0.5 kg, dv = 10 m/s, and dt = 0.2 s

got it :p that helped out