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# M2 Work Energy Power question. watch

1. This is a textbook question from Edexcel, Ch3 Ex3E Qu 8
A parcel of mass 5 kg is resting on a platform inclined at 25o to the horizontal. The coefficient of friction between the parcel and the platform is 0.3. The parcel is released from rest and slides down a line of greatest slope of the platform. Calculate:
a) The speed of the parcel after it has been moving for 2 s,
b) The potential energy lost by the parcel during this time.

What I tried was finding the friction force using f=uR then F=ma to find the acceleration. From here, u=0 a=2.9 t=2 v=? using v=u+at, I got v=5.8ms-1
The answer in the book says 2.95ms-1 and solution bank is no help

I'm pretty sure for b) you would use mgh1-mgh2 taking h2=0 at 2s after the parcel is released and finding initial h1 as s*sin(25)
3. Spoiler:
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4. (Original post by B_9710)
Yeah sure, let me just take a picture
5. (Original post by EricPiphany)
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you mustn't show him everything Eric

6. (Original post by the bear)
you mustn't show him everything Eric

well there's no point taking it down now that you quoted it...
anyways there's part b that he's going to need help with too...
7. Ok here, sorry for the delay. my phone decided to die on me D:
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8. b) the loss of GPE = increase in KE + work done against friction
9. (Original post by EricPiphany)
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Oh thanks, I see where I went wrong. When resolving for R, i used sin(25) rather than cos(25). Thanks for your help!
10. (Original post by the bear)
b) the loss of GPE = increase in KE + work done against friction
Ah yea, that seems a lot easier and quicker than the way i was going to do it. Thanks!

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