# Impulse/Momentum problems

1. Jul 3, 2006

### mikejones2000

I am currently stuck on two problems:
#1 A bat hits a moving baseball. If the bat delivers a net eastward impulse of 0.9 N-s and the ball starts with an initial horizontal velocity of 3.8 m/s to the west and leaves with a 5.3 m/s velocity to the east, what is the mass of the ball (in grams)?

I set J=deltaP
.9=95.3+3.8)m
m=.9/(5.3+3.8).

#The second problem has a force vs. time for an impulsive force graph and asks: The force shown in the figure below is the net eastward force acting on a ball. The force starts rising at t=0.012 s, falls back to zero at t=0.062 s, and reaches a maximum force of 35 N at the peak. Determine with an error no bigger than 25% (high or low) the magnitude of the impulse (in N-s) delivered to the ball. Hint: Do not use J = FΔt. Look at the figure. Find the area of a nearly equally sized triangle.

I am sure tthis problem is very simple but do not have a confident approach for some reason, I presume I find the time when it peaks at 35 N(.062-.012) and use this as my base? Then I would apply A=.5(35)(.062-.012)?

Any help would be greatly appreciated.

2. Jul 3, 2006

### G01

It seems like you methods are correct, is there a problem with you answers?

Also if this graph is the graph for the basball and bat in part one the area of your approximate triangle should be approximately .9Ns

3. Jul 3, 2006

### mikejones2000

I got 0.0989 for the first problem, im not sure if its in kilograms or grams and
0.875 for the second one. I know I got at least one problem out of the three assigned and presume it has to be one of these because the other is a multiple choice problem. Thanks in advance for any help.

4. Jul 4, 2006

### Kurdt

Staff Emeritus
If you're using SI units for your working it will be Kg.

With regards to question 1 remember that delta p is pf - pi. Also these are vector quantities but I think you've taken that into account just a reminder.

For question 2 if they say use a triangle then use a triangle it should be fine. The area under the curve would normally be determined by the integral of F(t) but since its not given the triangle method should give a fair approximation.

Last edited: Jul 4, 2006