# 2 Questions of Momentum and Impulse

wolfpack

## Homework Statement

Problem 1: A .145 kg baseball pitched at 40 m/s is hot on a horizontal line back to the pitcher at 52 m/s. If the contact time of the ball with the bat is 4.7e-3, calculate the magnitude of the average force acting on the ball due to the bat.

Problem 2:A billiard ball is moving at 3.1 m/s when it hits a stationary ball of the same mass. After the collision, the second ball moves at 2.4 m/s at an angle of 60.0 deg to the original line of motion, Find the magnitude and direction of the velocity of the first ball after the collision.

## Homework Equations

Problem1) Impulse= change in momentum=m(v1-v2)=F((delta t))
Problem2)p=m*v

## The Attempt at a Solution

My attempts at a solution are shown in the jpegs, with enumerated variables and equations I've tried. As for the method behind the madness, For problem one I am going off of the face that since impulse is the change is momentum, I can obtain a value from the quantifiable values for the momenta and then set the impulse equal to F delta t isolating the force in question.
For problem 2 I am going off of the conservation of momentum in a perfectly elastic collision. I know the enter of mass are uniform and masses are the same, and then I tried solving for the components of the momenta.
These questions are from the Andes OLI Learn by Doing series.

#### Attachments

• linmomentum.JPG
58.9 KB · Views: 386
• imp1.JPG
49.6 KB · Views: 367
Last edited:

Homework Helper
I can not follow your calculations, what have you got for the change of momentum in the first problem?

ehild

wolfpack
For the problem about impulse I have J=F (delta t)=delta p
F(t)=m(v2-v1)
F(4.7*10^-3)=.145(52-40)
Thus F=(.145(52-40))/(4.7*10^-3)=370.213 N
Apparently that is incorrect, but I am unsure of exactly what other equations to use with the quantities I have.

The change in momentum I got was (.145*52-.145*40)=1.74 (Kg*m)/s

Homework Helper
For the problem about impulse I have J=F (delta t)=delta p
F(t)=m(v2-v1)
F(4.7*10^-3)=.145(52-40)

You forgot that the initial and final velocities have opposite directions. If v1 is positive, v2 is negative. Think it over.

ehild

wolfpack
Ah I see what I did now, so with the revised computation the correct solution is 2838.298 N which I checked and it works. Thank you

I still have that momentum equation left for my OLI, I'm just rusty on collisions in two dimension in general. I know the resultant angles have some connection to the component angles of the momenta, but I'm really just not sure where to proceed.

Homework Helper
Find the velocity components parallel and normal to the original velocity. Apply sine and cosine of the given angle.

ehild