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# M2 Work done question: Where did I go wrong? Watch

1. The mark scheme did the whole "change in energy = wd by friction" which I understand but I don't understand how my method was incorrect..

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2. (Original post by creativebuzz)
...
You're going to hit yourself.

The weight is so your equation should be - then solve for .

That took me far too long to spot.
3. (Original post by Zacken)
You're going to hit yourself.

The weight is so your equation should be - then solve for .

That took me far too long to spot.
Hahah! Oh god that's so stupid of me!

But.. I still get 88.9N which isn't the right answer :/
4. (Original post by creativebuzz)
Hahah! Oh god that's so stupid of me!

But.. I still get 88.9N which isn't the right answer :/
How do you get that? Re-arranging: - so what do you get for ?
5. (Original post by Zacken)
How do you get that? Re-arranging: - so what do you get for ?

Ohhh because I divided!!! *facepalm**

Thank Zacken! I was freaking out because I thought my method was completely wrong but I didn't know why!
6. (Original post by creativebuzz)
Ohhh because I divided!!! *facepalm**

Thank Zacken! I was freaking out because I thought my method was completely wrong but I didn't know why!
Nope your method was perfectly fine, well done.

No problem.
7. (Original post by Zacken)
Nope your method was perfectly fine, well done.

No problem.
Such a relief!

Also,

do you mind explaining why the reaction forces act left and down? I'm still struggling to understand this and it's been soo long

8. (Original post by creativebuzz)
Such a relief!
Looks like Ghostwalker's going to answer that one, I'll let him do the honours. :-)

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