Find Magnitude: Help with Homework Problem

[nasadall]

Homework Statement

A ball of mass 350g is traveling with a speed of 4m/s when it hits at right angles a fixed vertical wall. The ball rebounds with a speed of 3m/s. Find the magnitude of the impulse exerted by the ball on the wall. Using a simple diagram show the direction of velocities and the impulse.

Homework Equations

m = 350g or m = 0.35kg v1 = - 4m/s^-1 v2 = 3m/s^-1

Magnitude = mv2 – mv1

The Attempt at a Solution

Magnitude = 0.35 3 – 0.35(- 4)

Magnitude = 1.05 – 1.4

Magnitude = - 0.35



Hi can some one check this equation for me please.

Also is there a unit to simbolize magnitude? and is the final answer 0.35 given in joules?

Last one how would i draw a simple diagram showing the direction of velocities and the impulse?

thank you

 

[Rick88]

Your final value is correct.
However, being a magnitude , it should have positive sign.

As for the units, just work them out by what you have in the equation.
I'm sure you know the units of m and v (and you're given them, anyway), so just use those.

Start drawing a diagram showing the velocities only, I'm sure you'll understand in what direction should the impulse go.

 

[nasadall]

i've calculated wrong.
it should have been.

Magnitude = 1.05-(-1.4)
= 2.45

2.45 is the final answer.

kg m/s

is the final answer given in N??

 

[Rick88]

N is kg m/s², but you only have kg m/s.

So you can either leave it as kg m/s or rewrite it as..?

 

[nasadall]

thank you for you help, but i can't get there, to be honest, i started studying after 15 years and this thing is doing my head, i have to handle my course work tomorroy, and I'm still half way.lollol

 

[Rick88]

Just look at how the RHS of the two equations below is altered and you will know how to change the LHS as well.

N = kg m/s^2

? = kg m/s

 

[nasadall]

i think the answer is Ns

 

[Rick88]

It is indeed.