A strange pre-test problem

[Simonpe]

Hi!

I have a big problem with this simple question. I can manage all the other questions on the paper i got except this one, and it's even one of the easier in there. So please gimme suggestions of what formulas to use:

A person is struggeling his way up a 8 degree hill with the velocity of 12km/h. Calculate the power use. The total mass of him and his bicycle is 75kg. Air resistance and friction is 5,0% of mg.

I tried calculating it with both force laws and energy laws and i end up with the answer 120W (or something i cant remember) but the correct answer should be 0,46kW

Please excuse my bad english, and thanks for the help!

Simon

[Doc Al]

Welcome to PF!

Show us how you got your answer and we'll give you a hand.

[Simonpe]

Thanks!

Unfortunately i've erased the first soultion and i've only got a lot of unreadable panic notes left :P but can u at least tell me what path to use, Energy or Force? Then i think i'll be able to solve it.

Thanks in advance!

[Doc Al]

Both methods should agree. Go ahead and use the "force" method. :smile:

[Simonpe]

I think i'll manage it now, after hours of studying. Got a test tomorrow morning and i got a little scared that i couldn't accomplish a simple task like that. Btw i used the energy method but thanks for the advice :D

take care and good night