# A 60 kg skateboard rides towards a hill with a speed of 8 m/s?

Calculate their kinetic energy.

If they ride up the hill, what will their total energy be at the midway point?

If they reach the top of the hill with a speed of 4 m/s, how high is the hill?

### 1 Answer

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- billrussell42Lv 72 months ago
1) KE = ½mV² = ½60•8² = 30•64 = 1920 J

2) need height of hill

3) KE at top = ½60•4² = 30•16 = 480 J

KE lost = 1920–480 = 1440 J

that is equal to PE at top of hill

PE = mgh = 1440 = 60•9.8•h

h = 2.45 m

back to 2:

half way is 1.22 m

PE at that point is mgh = 60•9.8•1.22 = 717 J

lost energy = 1920 – 717 = 1203 J, which is KE

KE = ½mV² = ½60•V² = 1203

V² = 1203/(30)

V = 6.33 m/s

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