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I'm not getting some mechanics questions. I'm sure that I'm right... but the answer in the back of the book is different. I'll type it out for you guys

First Question:

"A body of mass 2kg is held in limiting equilibrium on a rough plane inclined at 20 degrees to the horizontal by a horizontal force X. The coefficient of friction between the body and the plane is 0.2. Modelling the body as a particle find X when the body is on the point of slipping:

a) up the plane.

b) down the plane."

I done a, but got it wrong, so I left out b, since I'm assuming I'm missing something.

I got 11.05 N, but the answer says 11.9N

The Second question is:

"Given that the resistances total 400N find the magnitude of the constant force needed to accelerate a car of mass 800kg from rest to 20m/s in 15 seconds."

Okay so I work out a, which is a=(v-u)/t=20/15=4/3

So F=ma=800x4/3=1066.67N

F+Resistance=Total Force=1466.77N, but the answer is 1470N apparently?? I'm confused.

Would like this to be resolved as soon as possible cos I've got alot of mechanics questions to do.

Thanks :)