A child and sled with a combined mass of 48.6 kg slide down a frictionless hill that is 8.02 m high. If the sled starts from rest, what is its speed at the bottom of the hill?
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A person doing a chin-up weighs 755 N, disregarding the weight of the arms. During the first 25.0 cm of the lift, each arm exerts an upward force of 381 N on the torso. If the upward movement starts from rest, what is the person's speed at this point?
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A skier of mass 65.5 kg is pulled up a slope by a motor-driven cable. How much work is required to pull the skier 41 m up a 30° slope (assumed to be frictionless) at a constant speed of 2.0 m/s?
2007-12-16 12:43:41 · 1 answers · asked by Anonymous in Science & Mathematics ➔ Physics
1. Potential energy at the top equal to kinetic energy at the bottom (since there is no friction).
Pe=Ke
mgh=0.5 mV^2
V=sqrt(2mgh /m)
V= sqrt(2gh) (who cares amount the mass?)
2. Total energy gained
Pe= wh
Work done by both arms
W= 2Fh
Kinetic energy is
Ke= Pe- W
0.5mV^2= mgh - 2 Fh
V= sqrt( 2(mgh - 2 Fh)/m)
3. Pe= mgh
Pe= 65.5 x 9.81 x 41=26,300 J
2007-12-19 09:38:09 · answer #1 · answered by Edward 7 · 1⤊ 0⤋