work ? power?

Question

hello, i am having problems with one of my hw problems... i am going to change the numbers from the original so i have to work it out myself so if w/ the new numbers someone could explain and talk me through how to do it... such as if there is a formula to use or how to do it i would appreciate it... I'm not sure what i'm not grasping about this it seems like to others its a simple concept so there is something not clicking any help would be appreciated thank you.....

bicyclists with mass 70 kg generates average power of 5.50 W per kilogram of body mass..... how much work is done during 80 km race w/ avg speed 12.0 m/s


please explain thank you

Answer 1

Power = W/∆t (work over change in time)

If we rearrange this equation, Work = Power*Time

Since he's generating 5.50 Watts per kg, and he weighs 70 kg, then he's producing 385 Watts of power.

Now, riding 80 km at 12.0 m/s will take him 6666.67 seconds. Thus, the total work he exerts will be 385*6666.67 = 2566666.67 Joules.

If you're interested, you can find the average force he's exerting by dividing the total work by the distance, approximately 32 Newtons. Assuming he starts and ends at the same elevation, this is the force of drag and friction that he must overcome! (If he finishes at a higher elevation, then some of that work is also used to climb the hill.)

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For reference (as I strongly encourage dimensional analysis):
1 J = 1 N*m
1 Watt = 1 J/s = 1 N*m/s

Answer 2

Work = mv(squared)/2 (initial) - mv(squared)/2(final) Use this equation. For this you also need the initial speed of the cyclist. But you dont have that information. So i can't get the answer. Otherwise this equation can work perfectly!

Answer 3

you know that f=ma, or force = mass times acceleration, so
the 70 kg is the mass, and the speed is 12.
the force then is 0.84 newtons
then you multiply that by the distance to get a force of 0.0672 newtons.

The answer is 0.0672 joules