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# mechanics -- simple energy question watch

1. a child, mass 30kg slides down 5m down a playground slide inclined at 40 to the horizontal. Calculate the potential energy lost.

I did 30x9.8x 5sin40 = 1095J

However, answer sheet says its 945J?

Where have I gone wrong?
2. Edit: cocked it up, my apologies. Is there any mention of a resistive force etc?
3. (Original post by JumpingJonny)
sin 40 = 5/h therefore h = 5/sin40

Try using that and see how it goes
That is wrong.
4. you must take friciton into account
5. (Original post by SilverstarDJ)
a child, mass 30kg slides down 5m down a playground slide inclined at 40 to the horizontal. Calculate the potential energy lost.

I did 30x9.8x 5sin40 = 1095J

However, answer sheet says its 945J?

Where have I gone wrong?

6. When I put that in my calculator it comes out as 944.89J Check you have entered it correctly
7. (Original post by gilbo)
That is wrong.
Yeah I realised that once I had written it, hence the edit, the OP is actually correct, he just hasnt calculated it right.
8. (Original post by gilbo)

lol!!
9. aaah it's in radians and not degrees! Thanks.
10. (Original post by SilverstarDJ)
aaah it's in radians and not degrees! Thanks.
HAHA textbook schoolboy error.
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Is It A Crime Helping???

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12. and i have been negged again.....as if i really care
13. 3 negs on a single day....that must be a record

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