wo professional skaters (Joe and Sue) start their routine by pushing off from a
ID: 1317448 • Letter: W
Question
wo professional skaters (Joe and Sue) start their routine by pushing off from a facing, stationary pose as shown in figure (a). The kinetic frictional force acting on their skates can be ignored while they are pushing against each other, however once they separate, the force of kinetic friction eventually brings them to a halt. As shown in figure (b), after the push-off, they move in opposite directions with different speeds. The magnitude of their acceleration is the same, but Sue glides 3 times as far as Joe before coming to rest. Determine the ratio of their masses mS/mJ.
=
mS mJExplanation / Answer
Use conservation of momentum to relate their two initial speeds.
(m_1) (v_1) =(m_2) (v_2)
Then use conservation of energy to relate the initial kinetic energy with the energy dissipated by friction.
KE=(1/2)mv^2
TE=energy dissipated=(Force of friction)(distance)
The force of friction depends on two things, how rough the surfaces are and how tightly they are pressed together.
F=(mu)N
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