# Physics Homework

posted by Jenni

I have a few questions that I don't understand and would like to get checked, please?

5.If energy is conserved and momentum is conserved, would they both have to be conserved simultaneously in some interaction?

My answer: No because each engergy and momemtum is being conserverd.

9. A 60 kg skydiver moving at terminal speed falls 50m in 1 s. What power is the skydiver expending on the air?

My answer: p=work/time
p=50m/1s=50 Watt

12.Where, exactly, does the energy stored in oil come from? How can we get "work" from oil? In your discussion, try to use the words work, energy, heat, power, and conservation in their correct physical sense.

-I don't understand this question.

1. drwls

The answer to 5. is yes, but some of the energy may be heat and not show up in equations of motion. Only elastic collision conserve (kinetic + potential) energy.

9. Your equation is wrong. You cannot divide distance by time to get power. At terminal speed,
(powerloss) = weight x velocity.
The average power for the one second is M g/(1 sec)

12. The energy from oil starts with chemical energy in the molecules that gets converted to heat in an engine (by reacting with oxygen), and then converted to mechanical energy when a piston is pushed by hot combustion products.

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