# Homework Help: Magnitude of Impulse

1. Nov 24, 2005

### Elysium

Another question, this time I'm dead stuck:

I don't really understand the question nor the concepts implied. Can anyone give me an explaination and directions to the right equations? My physics textbook doesn't seem to have any information on the subject (or maybe it does in a different term). Does it have anything to do with the moment of inertia?

Thanx

2. Nov 24, 2005

### Gokul43201

Staff Emeritus
What text is this (looks a lot like a problem I remember from Cutnell & Johnson) ? Go to the chapter on momentum and start reading. You'll find the concept of Impulse explained right at the beginning.

3. Nov 24, 2005

### Elysium

The question isn't from my textbook at all. I have Physics for the biological sciences. Nothing in the book seems familiar to this problem, not even the terms.

4. Nov 24, 2005

### Gokul43201

Staff Emeritus
It should be covered in Ch. 8. "Mechanics of Biological Systems: Forces & Motion".

If not, read the introduction here. That's all you will need for this problem.

5. Nov 24, 2005

### Elysium

Ok, I've read a bit about momentum. So it's basically mass x times velocity and its dimension is force in a certain amount of time

So for a), when the ball hits the bat, it exerts a force on the bat for a certain period of time (which inthis problem we don't know)?

$$I = m \Delta v$$

$$I = 0.140 x 39$$
$$I = 5.5 \textin kg(m/s)$$

Last edited: Nov 24, 2005
6. Nov 24, 2005

### Elysium

I can't believe how easy this is.

for b)

$$F = \Delta t = m \Delta v\\ F = \frac{m \Delta v}{\Delta t}\\ F = \frac{5.5}{1.2}\\ F = 4.6 \textin {N}\\$$

and c)

$$a = \frac{F}{m}\\ a = \frac{4.6}{0.140}\\ a = 33 \ m/s^2\\$$

Last edited: Nov 24, 2005
7. Nov 25, 2005

### Gokul43201

Staff Emeritus
Okay...you've got the basic idea, but there's a couple things to point out.

a) $$\Delta v = v_f - v_i = 39 - (-39) = 78~ m/s$$

b) $$\Delta t = 1.2~ms=1.2 \times 10^{-3} ~s~,~~or~0.0012~s$$

8. Nov 25, 2005

### Elysium

I still have a few questions to finish, but I think I can handle them.

9. Nov 25, 2005

### Elysium

*bump*

sorry, but there's one last issue

I get $$6.6 \times 10^4 \textin{m/s^2}$$ as an answer. Does this large amount of acceleration make sense? I gather it's because of the very short length of time during the impulse?

Last edited: Nov 25, 2005
10. Nov 25, 2005

### Gokul43201

Staff Emeritus
Correct, on both counts.