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Bike problem

  • Thread starter griefcrack
  • Start date
I'm going through my end of the year exam papers, since I figured I should actually make an effort at school this year, well anyway I'm terrible at physics and this question stumped me. Heres a diagram ( I drew it in MS paint ha, I even included a helmet cause riding bikes without one ain't safe. )

http://img214.imageshack.us/img214/9627/lolbikemy1.gif [Broken]

While travelling home, the bike accelerates at 1.5 ms-2 over a distance of 25m as shown in the diagram.

Toni and the bike have a mass of 70kg.

(j) Using the equation F = ma, calculate the net force acting on the bike when it is accelerating.

(k) If it takes 5 seconds to cover the distance of 25m, calculate the power output of the bike during this time.

I think the answer for (j) is F = 70 x 1.5, so this gives me 105 N
Anyway I can't remember how I'm suppose to do (k) and my feeble attempts at doing it, gave me 13125 W but I'm sure thats wrong.
 
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Answers and Replies

cristo
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I think the answer for (j) is F = 70 x 1.5, so this gives me 105 N
That's correct
Anyway I can't remember how I'm suppose to do (k) and my feeble attempts at doing it, gave me 13125 W but I'm sure thats wrong.
What did you do to get this answer? Please show your work, as we can't see whether you're wrong if we can't see what you've done!
 
Thanks for replying so quickly, the other formula ( I think ) would be P = E x T and W = F x d, so I'm assuming W = 105 x 25 giving me 2625. Then P = 2625 x 5 giving me 13125 W.
 
cristo
Staff Emeritus
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Thanks for replying so quickly, the other formula ( I think ) would be P = E x T and W = F x d, so I'm assuming W = 105 x 25 giving me 2625. Then P = 2625 x 5 giving me 13125 W.
Your equation W=Fd is correct, and so is your numerical value of 2625. However, power is the rateof doing work, so your second equation is P=W/t.
 

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