A 33.0-kg girl stands on a 13.0-kg wagon holding two 13.5-kg weights. She throws
ID: 2142933 • Letter: A
Question
A 33.0-kg girl stands on a 13.0-kg wagon holding two 13.5-kg
weights. She throws the weights horizontally o? the back of
the wagon at a speed of 5.0 m/s relative to herself. Assuming
that the wagon was at rest initially.
a) what is the speed of the girl relative to the ground after she throws both weights at
the same time?
b)Assuming that the wagon was at rest initially, what is the
speed relative to the ground with which the girl will move
after she throws the weights one at a time, each with a speed
of 5.0 m/s relative to herself?
Explanation / Answer
1)Perhaps relative to the girl means relative to the girl WHILE she is in motion.
In this case, if the girl's motion relative to the ground is called v, the speed of the weights relative to the ground will be 5 - v. (Because the sum of the velocity of the weights and the girl must equal 4 m/s)
Momentum -->
(5m/s - v)*(13.5kg + 13.5kg) = (33 kg + 13 kg)*v
135m/s* kg - 27vkg = 46vkg
135m/s* kg = 73v kg
v = 1.8493 m/s
Thus the girl & wagon move with a velocity of 1.8493 m/s?
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