Collision and Impulse, Linear Momentum

[kappcity06]

can someone help? I have no isea how to do this problem.

A force in the negative direction of an x-axis is applied for 21 ms to a 0.40 kg ball initially moving at 10 m/s in the positive direction of the axis. The force varies in magnitude, and the impulse has magnitude 32.4 Ns.

(a) What is the ball's speed just after the force is applied? m/s

(b) What is the average magnitude of the force? N

 

[Doc Al]

Tell us what you know about impulse, momentum, and the impulse-momentum theorem.

 

[kappcity06]

i know about elastic and inelastic collsions

 

[kappcity06]

i know the formula for those

 

[kappcity06]

i know p=mv

 

[Doc Al]

They gave you the impulse. What does that tell you?

 

[kappcity06]

p1i+p2i=p1f+p2f

 

[kappcity06]

i should use p=mv

but thsat would give be AN INTIAL SPEED OF 81

32.4=.4v

 

[Doc Al]

impulse-momentum theorem

Impulse = $\vec{F}_{ave} \Delta t = \Delta \vec{p} = m \Delta \vec{v}$

 

[kappcity06]

that gives me 91

32.4=.4(v-10)

 

[Doc Al]

What's the direction (and thus sign) of the impulse compared to the direction of the initial velocity?

 

[kappcity06]

negative to the x-axis then postivite the force is positive

 

[Doc Al]

Answer these questions:
What's the direction of the initial velocity?
What's the direction of the impulse?
What's the direction of the change in velocity?
What's the direction of the final velocity?

 

[kappcity06]

the direction of the intial volcity is positve.
the direction of the impulse is negative
the direction of the change in velocity is negative

the direction of the final velocity is negative

 

[Doc Al]

Good. So you should have no problems calculating the final speed.

 

[kappcity06]

ok thank you

 

[thiotimoline]

After my analysis, first get the initial momentum of the ball in the positive x-direction. Second, get the force applied on the ball in the negative x-direction. Impulse is mass x change in velocity. Problem is whether the total force acting on the ball is sufficient to change the direction of ball.