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# M2 - power watch

1. Hey, I have got an answer to this question very close to the one in the answers- I get 25410 and they get 25400, so they may be giving it to 3SF, but would just like someone to check my working...

A lorry of mass 15000kg is moving up a straight road inclined at an angle x to the horizontal where sinx=0.25.
The lorry is travelling at aconstant speed of 12m/s and the constant resistance to its motion has mag 175kN.
Find the work done in 10s by the engine of the lorry.

My working:
(F is driving force up slope)

resolve parallel to slope:
F-175000- 0.25x15000g = 15000 x 0
F = 211750

Power = Fv
= 211750 x 12
= 2541000

Since power is work done per s, work done in 10s = power x 10,
= 25410000 W
= 25410 kW

thank you!!!
2. Looks good to me.
3. Probably just a printing error - there's LOADS in my GCSE textbook. I suspect that they put in the odd false answer to try and catch cheaters out (answers are at the back of the book)
4. (Original post by franks)
Hey, I have got an answer to this question very close to the one in the answers- I get 25410 and they get 25400, so they may be giving it to 3SF, but would just like someone to check my working...

A lorry of mass 15000kg is moving up a straight road inclined at an angle x to the horizontal where sinx=0.25.
The lorry is travelling at aconstant speed of 12m/s and the constant resistance to its motion has mag 175kN.
Find the work done in 10s by the engine of the lorry.

My working:
(F is driving force up slope)

resolve parallel to slope:
F-175000- 0.25x15000g = 15000 x 0
F = 211750

Power = Fv
= 211750 x 12
= 2541000

Since power is work done per s, work done in 10s = power x 10,
= 25410000 W
= 25410 kW

thank you!!!
actually, all the answers at the back are given to 3 sig figures
5. actually, all the answers at the back are given to 3 sig figures
really?! lol, shows how much attention I pay !!!
6. Why is Work done given in Watts, rather than in Joules?

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Updated: February 14, 2013
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