# Homework Help: Impluse problem

1. Mar 9, 2005

### whereisccguys

Recent studies have raised concern about heading' in youth soccer (i.e., hitting the ball with the head). A soccer player heads' a size 4 ball, deflecting it by 52.0°, and keeps its speed of 10.00 m/s constant. A size 4 ball has a mass of approximately 0.302 kg. What is the magnitude of the impulse which the player must impart to the ball?

(part b)
If the player's head has a mass of 3.80 kg, what is the magnitude of the average acceleration of the player's head during the impact? Assume that over the brief time of the impact, 27.90 ms, the player's head can be treated separately from the player's body.

um... i'm not really sure how to start the problem
i only know that impulse is the the change in momentum pf - pi... i dunt see how this would tie in with the problem, any help would be appreciated

2. Mar 9, 2005

I too am having difficulty on this one

3. Mar 9, 2005

### Staff: Mentor

Well, since they ask you for the impulse, I'd say it ties in quite nicely.

Impulse = $\Delta (m\vec{v})$. Draw a diagram of the initial and final velocity vectors and subtract them. Find the magnitude of the impulse.

Once you've found the impulse, then use:
Impulse = $F \Delta t$ to find the average force. Then use Newton's 2nd law to find the acceleration.

4. Mar 9, 2005

Alright, I did that. My numbers are that the mass of the ball is 0.252 kg, it was deflected by 39 degrees, and the velocity of the ball is 18.8 m/s. I found that the Impulse = 2.05 kg*m/s. That is not correct with the computer. What am I doing wrong?

5. Mar 9, 2005

### whereisccguys

i got the right answer thanks a lot Doc Al

6. Mar 14, 2005

### Punchlinegirl

The angle is confusing me. Do you have to use that somewhere to find the impulse?

7. Mar 15, 2005

### Staff: Mentor

Yes, you need to know the angle in order to determine the change in velocity. Remember, velocity is a vector.

8. Mar 24, 2005

### AcuraRacer32tl

Hopefully this isn't too late. I did the exact same mistake. I believe you subtracted the two vectors wrong. You should use the law of cosines which is c^2 = a^2 + b^2 - 2*a*b*cos(45) then multiply by m.

You should get an answer around 5.____

Hope this helps.