What is Drew's velocity after he throws Lily?

Question

Two ice-skaters stand in the middle of an ice rink. Drew has a mass of 75 kg, and Lily has a mass of 55 kg. Drew holds Lily, and they are both stationary. To begin their routine, he tosses her forward with a speed of 2 m/s

a. What is Drew's velocity after he throws Lily? (2 points)

0 = 75kg * v + 55kg * 2m/s

v = -1.5 m/s (that is, backwards)

b. Later in the routine, Drew is holding Lily in his arms while they skate forward at a speed of 5 m/s. After he throws her forward at a speed of 2.5 m/s (relative to their initial velocity), how much does he slow down? (2 points)

Answer 1

I agree with your answer for part (a).

Part (b):

Initial momentum:

(75 + 55)(5) kg m/s

Final momentum:

v = Drew's final speed

75v + 55(5 + 2.5) kg m/s

Set initial and final momentum equal, solve for v (Drew's final speed), and compare the result to Drew's initial speed of 5 m/s. You should be able to finish from here.