# Tennis Ball and Impulse!

amazondog

## Homework Statement

A tennis ball of mass m = 0.087 kg and speed v = 43 m/s strikes a wall at a 45° angle and rebounds with the same speed at 45° (Fig. 7-29). What is the impulse given the wall?

## Homework Equations

Impulse = M x V
Sin (theta) = opp/hyp

## The Attempt at a Solution

Impulse = .087(43) = 3.741 (at 45 degrees)

Sin(45) = x / 3.741
x = 3.1832 Is the impulse given the wall. Is this corect?

Mindscrape
Impulse is change in momentum. Momentum is mass times velocity. What you've found is momentum in the y direction.

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amazondog
Is there change in momentum though? Cause its going the same velocity.

Mindscrape
Same speed or same velocity?

amazondog
same speed, different velocity. But because the angles, speeds, and masses are the same don't they cancel?

Mindscrape
Which velocities will cancel and which ones won't? You've got two components.

amazondog
So the x and y components are both 30.4. That would be the x component cancels (30.4-30.4) but the y component would double because its going upwards..?

Mindscrape
Actually it's the other way around. Let's call up and right positive, and say the ball hits the wall traveling to the the right. It hits the wall and continues up
$$\Delta p_y = mv_fy - mv_iy = m(30.4-30.4) = 0$$
while in the x direction it rebounds and goes the other way
$$\Delta p_x = mv_fx - mv_ix = m(30.4-(-30.4))= m*60.8$$