# Energy, work &power physics help!!?

50. While running, a person dissipates about 0.60 J of mechanical energy per step per kilogram of body mass. If a 60-kg person develops a power of 70 W during a race, how fast is the person running? Assume a running step is 1.5 m long.

51. Water flows over a section of Niagara Falls at the rate of 1.2 * 10^6 kg/s and falls 50 m (Fig P5.51). How much power is generated by the falling water?

show me step by step how to get the answer plz

ty :D

Relevance

(50) Want to get to m/s:

.6J/(step)(kg)* 60 kg = 36J/step

(36J/step) * (1 step)/ 1.5 meters =24J/m

70w=70J/s

Vel=(70J/s )*(1m/24J)=2.916m/s

(51) power=energy/time

potential energy=mass*gravity acceleration*height

We don't have mass but we have mass/s, which is good enough because if we pick a time, say 10 secs worth of water, then we would have to divide by 10 anyway to get the power.

power=(1.2*10^6)(9.8)(50)=5.88*10^8 J/s

Check the math, etc. It's been a while...

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