A sled and a rider with a combined mass of 50·kg are at the top of a hill, 10·m

Question

A sled and a rider with a combined mass of 50·kg are at the top of a hill, 10·m above ground level. The sled is given a push, providing an initial KE (for the sled and rider) of 1700·J at the top of the hill. Use g=10·m/s2. (a) Choosing a reference level at the bottom of the hill, what is the PE of the sled and rider at the top of the hill? Correct: J. (b) After the push, what is the total mechanical energy of the sled and rider at the top of the hill? Incorrect: J. (c) If friction and air resistance can be ignored, what will be the KE of the sled and rider at the bottom of the hill? Correct: J. (d) Compared to your answer for the previous part, how much KE would the sled and rider have if friction and air resistance cannot be ignored? Choose one answer only. more KE KE could be more, less, or the same same KE less KE

Explanation / Answer

a) Initial potential energy = m*g*h

= 50*10*10

= 5000 J

b) After push, total mechancal energy = potentail energy + kientic energy

= 5000 + 1700

= 6700 J

c) Kinetic energy at the bottom = 6700 J (because here potentail energy is also converted into kinetic energy)

d) less KE

because, some energy is lost in the form of heat.

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