Hello, I recently arrived at a new school and I was put into a Physics class. I was in American History and English before this, so I was head first into a difficult subject with no basics down.(adsbygoogle = window.adsbygoogle || []).push({});

I am currently working my hardest on these problems and need to know if I am doing it correctly.

Question: What is the average power supplied by a 60.0 kg secretary running up a flight of stairs rising vertically 4.0 m in 4.2 s?

Now, I know that I will be using power(P=W/T) and work(W=FD) equations, so I rewrote it as:

P=W/T=Fd/t which also equals mgd/t

so I then just substituted:

(60.0kg)(9.81m/s)(4.0m)/4.2 s and since kg/m/s is J and J/s is W, the answer I got is 560.57 W.

Question: A 16.0 kg child on roller skates, initially at rest, rolls 2.0 m down an inclin at an angle of 20.0(degrees) with the horizontal. If there is no friction between incline and skates, what is the kinetic energy of the child at the bottom of the incline?(g=9.81 m/s(sup 2))

So, I guess I am going to need kinetic friction equation KE=1/2mv(sup 2).

Now I have the mass, but how do I go about finding the speed?(Hints please, no answers, I want to try and solve and understand :-))

Question: A 40.0 N crate at rest slides down a rough 6.0 m long ramp inclined at 30.0(degrees) with the horizontal. The force of friction between the crate and ramp is 6.0 N. Find the velocity of the crate at the bottom of the slide.

This one I am confused about. I don't even know how to start this one.

Sorry for having such little understanding, but I am trying my hardest. Thanks for any help in adavnce!

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Work, power, and kinetic energy

**Physics Forums | Science Articles, Homework Help, Discussion**