- #1
FaNgS
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This is a problem about relative velocities and conservation of momemtum.
Here is how the problem goes:
A 39.7 kg girl is standing on a 101 kg plank. The plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless supporting surface. The girl begins to walk along the plank at a constant speed of 1.58 m/s to
the right relative to the plank.
(a)What is her velocity relative to the ice surface?
(b)What is the velocity of the plank relative to the ice surface?
Working:
The way I'm thinking is that since the girl is moving to the right with a speed v=1.58 m/s then the plank moves (after being at rest) with the same speed v=1.58m/s but in the opposite direction (left) so its more like that the speed of the plank is -1.58 m/s.
Considering that, the ice surface is moving to the right with the same but opposite speed v, which is then 1.58 m/s.
Kinda sounds weird to me. I tried using conservation of momemntum also and said that:
(39.7)(1.58) + (101)(0) = 39.7(V) + (101)(-1.58)
then V is about 5.59 m/s
Please advise
As for part B, i haven't been able to figure that one out. I don't know if conservation of momentum should be used or some other method to solve it.
Help is greatly appreciated
Your truly,
Fangs
Here is how the problem goes:
A 39.7 kg girl is standing on a 101 kg plank. The plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless supporting surface. The girl begins to walk along the plank at a constant speed of 1.58 m/s to
the right relative to the plank.
(a)What is her velocity relative to the ice surface?
(b)What is the velocity of the plank relative to the ice surface?
Working:
The way I'm thinking is that since the girl is moving to the right with a speed v=1.58 m/s then the plank moves (after being at rest) with the same speed v=1.58m/s but in the opposite direction (left) so its more like that the speed of the plank is -1.58 m/s.
Considering that, the ice surface is moving to the right with the same but opposite speed v, which is then 1.58 m/s.
Kinda sounds weird to me. I tried using conservation of momemntum also and said that:
(39.7)(1.58) + (101)(0) = 39.7(V) + (101)(-1.58)
then V is about 5.59 m/s
Please advise
As for part B, i haven't been able to figure that one out. I don't know if conservation of momentum should be used or some other method to solve it.
Help is greatly appreciated
Your truly,
Fangs