Momentum Question: Calculating Velocity on a Rolling Platform

[runningirl]

Homework Statement

Stevie stands on a rolling platform designed for moving heavy objects. The platform has mass of 76 kg and is on a flat floor, supported by rolling wheels that can be considered to be frictionless. Stevie's mass is 43 kg. The platform and Stevie are stationary when she begins walking at a constant velocity of +1.2 m/s relative to the platform. (a) What is the platform's velocity relative to the floor? (b) What is Stevie's velocity relative to the floor?

Homework Equations

The Attempt at a Solution

the answers are supposed to be:
a)-.43 m/s
b) .77 m/s

i don't understand how they got this. but my main question is what do they mean in REGARDS TO?

thanks!

 

[cdotter]

The frictional force from Stevie's shoes will move her forward. The frictionless platform has no friction and will move in the opposite direction.

Both questions will be solved by equation of momentum (i.e., $m_1v_1=m_2v_2$).

A) Stevie is moving at +1.2 m/s and her movement causes the platform to move. The moving platform has Stevie standing on it so you will have to account for both masses and also the fact that it is moving in the opposite direction of Stevie.

B) The platform has a mass and is moving at the velocity you found in part A. Stevie has a mass and is moving in the opposite direction of the platform.

 

[runningirl]

i know this sounds dumb, but I'm not sure what to do with what you told me :(