Simple Power calculation

1. Mar 7, 2012

MMCS

Can anyone see where i have went wrong? I keep getting the same wrong answer.

A 1100 kg car accelerates from rest reaching a distance of 110 m in 8.7 seconds, determine the average power in KW required to achieve this acceleration (your answer should be to 2 decimal places).

ANS = 40.43
MY ANS = 20.21

Working out

V = d/t
V= 110/8.7 = 12.64

Acc = (12.64 - 0) / 8.7 = 1.45

Force = ma
Force = 1100 x 1.45 = 1598.63

Work done = force x distance
Work done = 1598.63 x 110 = 175848

Power = WD/T
Power = 175848/8.7 = 20.21KW

Thanks

2. Mar 7, 2012

th4450

The velocity is not constant here,
you should use s = ut + $\frac{1}{2}$at2 instead

3. Mar 7, 2012

MMCS

Thanks for your reply.
How do i use this formula if i have two unknowns for V and a

4. Mar 7, 2012

th4450

You just have to find a and carry on with F=ma

P.S. I gave you the wrong formula just now :P

5. Mar 7, 2012

MMCS

Got it, thanks mate

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