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4. (25 pts) A child rides a sled from rest starting from the top of a snow-covered hill. The vertical height (not length) of the hill is 7.20 m from the base to the top. The child plus sled have a combined mass of 55.0 kg. (a) If the hill and sled were frictionless, what speed would the child have at the bottom of the hill? (b) The measured speed of the child at the bottom of the hill turns out to actually be 9.50 m/s (probably not what you found in part (a)). How much work did the force of friction do on the sled/child on the trip down the hill? Assume friction is the only non-conservative force acting. (c) If the hill is smooth and straight with an angular slope of 20°, what is the coefficient of kinetic friction between the hill and the sled? 

          4. (25 pts) A child rides a sled from rest starting from the top of a snow-covered hill. The vertical height (not length) of the hill is 7.20 m from the base to the top. The child plus sled have a combined mass of 55.0 kg.

(a) If the hill and sled were frictionless, what speed would the child have at the bottom of the hill?

(b) The measured speed of the child at the bottom of the hill turns out to actually be 9.50 m/s (probably not what you found in part (a)). How much work did the force of friction do on the sled/child on the trip down the hill? Assume friction is the only non-conservative force acting.

(c) If the hill is smooth and straight with an angular slope of 20°, what is the coefficient of kinetic friction between the hill and the sled?
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4. (25 pts) A child rides a sled from rest starting from the top of a snow-covered hill. The vertical height (not length) of the hill is 7.20 m from the base to the top. The child plus sled have a combined mass of 55.0 kg. (a) If the hill and sled were frictionless, what speed would the child have at the bottom of the hill? (b) The measured speed of the child at the bottom of the hill turns out to actually be 9.50 m/s (probably not what you found in part (a)). How much work did the force of friction do on the sled/child on the trip down the hill? Assume friction is the only non-conservative force acting. (c) If the hill is smooth and straight with an angular slope of 20°, what is the coefficient of kinetic friction between the hill and the sled?

Added by Robert C.

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University Physics with Modern Physics
University Physics with Modern Physics
Hugh D. Young 14th Edition
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A child rides a sled from rest starting from the top of a snow-covered hill. The vertical height (not length) of the hill is 7.20 m from the base to the top. The child plus sled have a combined mass of 55.0 kg. If the hill and sled were frictionless, what speed would the child have at the bottom of the hill? (b) The measured speed of the child at the bottom of the hill turns out to actually be 9.50 m/s (probably not what you found in part (a)). How much work did the force of friction do on the sled/child on the trip down the hill? Assume friction is the only non-conservative force acting. (c) If the hill is smooth and straight with an angular slope of 20°, what is the coefficient of kinetic friction between the hill and the sled?
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Transcript

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00:01 Hello everybody, we see that when the body say is at the top of this position h, so the total potential energy will be mg into h.
00:13 Now that potential energy will be converted to kinetic energy, through the motion will be converted and here it will be maximum means total energy will be converted and will be half mvmax square.
00:25 Now from conservation of energy principle half mvmax square is equal to mgh and from here we find vmax is equal to 11 .88 meter per second.
00:41 Now it happens when there is no dissipative force acting in the system.
00:46 This is part a.
00:49 Now in part b we see that if the speed is instead of 11 .88 meter per second is 9 .5 meter per second then there must be some work done by the friction and that work done will be equal to mgh minus half mv square and here the v will be 9 .5 meter per second.
01:17 Now it will become 1398 .925 that much joule that is the work done by friction...
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