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# M1 Exam Small Question watch

1. Particles A and B, of mass 2m and m respectively, are attached to the ends of a light inextensible string. The string passes over a smooth pulley fixed at the edge of a rough horizontal table. Particle A is held on the table, while B rests on a smooth plane inclined at 30 degrees to the horizontal.
The particle A is released from rest and begings to move.

What is the equation of motion of A and B, when the system is released from rest?

A's fine, just having a bit of trouble with finding B.
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2. Doc122.doc (19.0 KB, 95 views)
3. The particles will have the same acceleration?
4. I know. But could you give me the equations of motion?

I need to know about the sin's and cos's.

5. Let T be the tension in the string

Mass A is on a rough table, so has a coefft of friction µ.

Mass B in on a smooth pane, so no friction and force down the plane is mg.sin30°.

Mass A
Fr = µ.2mg
T - Fr = m.a
T - µ.2mg = 2m.a
===========

Mass B
mg.sin30° - T = m.a
½mg - T = m.a
=========

½mg - µ.2mg = 3m.a
3a = ½g - 2µg
a = g(1 - 4µ)/6
=========
6. Cheers. Big help mate.

7. (Original post by Fermat)
Mass B
mg.sin30° - T = m.a
½mg - T = m.a
=========
I thought it would be cos? Why isn't it?
I thought it would be cos? Why isn't it?
why do you think itd be cos?
9. When you resolve the forces on the block due to its weight, the normal reaction is mg.cosø and the force down the plane is mg.sinø.
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