What is the Impulse and Average Force in a Collision between a Ball and Wall?

[Ready2GoXtr]

Homework Statement

A 300g ball with a speed v of 6.0m/s strikes a wall at an angle theta of 30 degrees and then rebounds with the same speed and angle. It is in contact with the wall for 10ms. In unit-vector notation, what are (a) the impulse on the ball from the wall and (b) the average force on the wall from the ball?

http://ready2goxtr.googlepages.com/problem936.jpg

Homework Equations

Pi = Pf

Delta (P) = I
P = mv
<v being a vector>

Favg = I / (delta T)

The Attempt at a Solution

m = .3kg v = 6m/s theta = 30 degrees t = 10ms = .01s

a) Pi = PF

Pi = .3kg(Vcos(-30) i + Vsin(-30) j) = .26 kg * m/s i - 3 kg * m/s j

Pf = .3kg(Vcos(30) i + Vsin(30) j) = .26 kg * m/s i + 3 kg * m/s j

I = Delta (P) I = PF - PI

PF - PI = 6 kg * m/s j


b) I = sqrt(a^2 + b^2)
6kg * m/s / .01s = 600 N



I know i did it wrong. And thank you ahead of time.

 

[Doc Al]

Pi = .3kg(Vcos(-30) i + Vsin(-30) j) = .26 kg * m/s i - 3 kg * m/s j

Pf = .3kg(Vcos(30) i + Vsin(30) j) = .26 kg * m/s i + 3 kg * m/s j

Double check your arithmetic.

 

[Ready2GoXtr]

whats wrong with it? Sorry if I am a bit slow, all the chemotherapy i had last year sort of slowed me down i think.

 

[Doc Al]

whats wrong with it?

For example: .3*6*sin(30) = ?

 

[Ready2GoXtr]

Oh Duh me. 0.9 but still, I highly doubt that I = 1.8 kg * m/s J

 

[Ready2GoXtr]

well in that case I = 1.9 kg * m/s J and Favg = 180 N

 

[Ready2GoXtr]

Okay so that must be right answer then?

 

[Doc Al]

Sounds good to me. Express your answers using unit vectors.

 

[Ready2GoXtr]

Do i need to open up a new post for a new question?

 

[Doc Al]

Do i need to open up a new post for a new question?

In general: If it's a new problem, use a new thread. If it's a followup question on the same problem, ask it here.