What Is the Change in Linear Momentum of a Superball During Collision?

[lukejian]

Homework Statement

A superball with a mass of 83.6 g is dropped
from a height of 3.1 m. It rebounds to a height
of 2.5 m.
The acceleration of gravity is 9.8 m/s2.
What is the change in its linear momentum
during the collision with the floor? Answer in unit
of kg m/s.

Homework Equations

P=mV P=momentun m=mass V=velocity
changing P = F X changing time.

The Attempt at a Solution

the question asks the momentun during the collision with the floow, so P=mV
we know the m is 83.6 g . and do not know the velocity.
How do i get the velocity with above known vaule?

 

[lukejian]

i don't get this question, can someone helps me?

 

[lukejian]

Thanks

 

[awvvu]

Use kinematics (or energy) to determine velocity when it hits the floor.

Think about what it means to rebound with some height. What is the velocity when it rebounds to 2.5m? How can you determine the velocity it rebounded with?

 

[lukejian]

how can i determine the velocity when it rebounded?

 

[awvvu]

You have all the information you need to use one of the kinematics equations.

Initially the ball is at x = 0 with velocity v (which you want to solve for). It is later at x = 2.5 with 0 velocity.

 

[lukejian]

so what's the exact solution? i am confuse...

i understand what you are talking about, but how do i calculate the velocity going down?

 

[awvvu]

You're calculating the upwards velocity when it bounces. Hint: v^2 = v_0^2 + 2 a \Delta x

 

[lukejian]

oh so.. the initial velocity is 9.8, and the final velocity is 0 right?

and then the changing velocity is final - initial?

 

[awvvu]

Nono, your unknown IS the initial velocity.

 

[lukejian]

can i please have your msn or some kind of instant tool to communicate?

 

[awvvu]

can i please have your msn or some kind of instant tool to communicate?

We're really close to finishing this... I've even given you the formula to use.

You want to solve for v_0. v is the final velocity, a is the acceleration, and delta x is how far it's travelled.

 

[lukejian]

i got this already, i asked my teacher on MSN to find out..

the solution is actually finding the momentum downwards + upwards.

S=1/2at^2 and use V=at. and i got V.