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# M1 Help really stuck on this question. Please watch

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1. A particle of mass m kg is moving with constant speed 10 ms-1 across a smooth horizontal surface when it encounters a rough area, 20 m wide, where the coefficient of friction is 0.2.
Calculate:
(a) the acceleration of the particle (3)
(b) the speed with which the particle leaves the rough area (2)
(c) the length of time it takes for the particle to cross the rough area. (2)
2. You can figure out the acceleration by

F= uR=ma

And the reaction force is = the weight of the particle

Because R = mg and

You get umg = ma
The Masses cancel and you can find out the acceleration
The rest is suvat
3. a) Fmax = muR = 0.2 x mg

F (resultant force) = 0 - (0.2mg) = ma therefore, a = -0.2g

b) s=20, u=10, v=?, a=-0.2g, t?

c) More suvat
4. (Original post by TheBrownGuy)
A particle of mass m kg is moving with constant speed 10 ms-1 across a smooth horizontal surface when it encounters a rough area, 20 m wide, where the coefficient of friction is 0.2.
Calculate:
(a) the acceleration of the particle (3)
(b) the speed with which the particle leaves the rough area (2)
(c) the length of time it takes for the particle to cross the rough area. (2)
For part a, wouldn't mg = R (the reaction force) because it's not falling through the ground, and then -Fmax = ma, but Fmax equals the coefficient of friction multiplied by R so you would have -0.2mg = ma. Divide both sides by m and then you get a = -0.2g. I may have messed up on the directions but I think that's how you would do the first part. The other questions are just suvat equations I think.
5. (Original post by OrionMusicNet)
For part a, wouldn't mg = R (the reaction force) because it's not falling through the ground, and then -Fmax = ma, but Fmax equals the coefficient of friction multiplied by R so you would have -0.2mg = ma. Divide both sides by m and then you get a = -0.2g. I may have messed up on the directions but I think that's how you would do the first part. The other questions are just suvat equations I think.
Thanks

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