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# Confused on MEI M2 Work Energy Power question... watch

1. Ok heres there Question:

A cyclist of mass 84kg is travelling, initially, at a steady speed of 5m/s for 100m against a constant resistance of 49N
(i) find the work done against resistance.
Work done = Fd = 49*100 = 4900Nm
She now travels at a steady speed of 5m/s up a constant slope at an angle arcsin( ) to the horizontal, there is still a constant resistance of 49N
(ii) show power is 441W
resolved forces to get = 441
Travelling at 5m/s she now comes to another horizontal section and maintains her power, after three seconds her speed is 6m/s
(iii) explain why the driving force is not constant
fv=p, if p is constant and v changes, so must f
(iv) calculate the total work done against the resistance to motion during the three seconds
heres where I need help
this is what i did...

therefore 441*3 = 1323, but the answer in the back is 861... What am I doing wrong?
Thanks
2. (Original post by Tim_Lehner)
....
You've worked out the total work done in the 3 seconds which is the sum of the work done against resistance PLUS the work done in accelerating from 5 to 6 ms-1. So if you subtract the latter (change in K.E.) you'll end up with the correct answer.
3. cool, thanks

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