# I need help on this physics problem!?

If the speed of a 58 kg skier at 15 m up on a hill is 2.5 m/s, and the conversion from potential energy to kinetic energy as she skies down the hill is 65% efficient, then her speed when she skis down to 3 m will be __ m/s and __ kJ of energy will have been lost due to friction.

### 1 Answer

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- FiremanLv 73 weeks ago
1) Net PE to be utilized = mgΔh = mg x (12-3) = 9mg J

The KE avilable at the 3m mark = 9mg x 65/100 = 5.85mg J

Let the velocity at 3m mark is v m/s,

=>1/2mv^2 = 5.85mg

=>v = √[2 x 5.85 x 9.8]

=>v = 10.71 m/s

2) Loss of energy due to friction = 35% of PE utalized

=>ΔE(loss) = 35% of 9mg = 0.35 x 9 x 58 x 9.8 = 1790.46 J

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