# Physics

Two blocks A and B are connected by a light in extensible cord passing over a frictionless pulley. Block A starts from rest and moves up the smooth plane which is inclined at 30 degrees to the horizontal. Calculate at the moment that A has moved 4 m along the plane.

(a) the total kinetic energy of the system
(b) the speed of the blocks A and B

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1. The picture is not complete.

Are the two blocks identical (in mass) ?
Does block B hang free?

If it is, B will descend as A moves up.

Draw the free body diagram of each block.

Let the tension in string be T.
mass of each block = m
acceleration due to gravity = g
angle of incline = θ = 30°

Distance moved = s = 4m

Change in potential energy of system, δep
mgs(sinθ)-mgs
=mgs(sinθ-1)

Assuming no frictional and air-resistance loss,
δep+δek=0, or
δek=mgs(1-sinθ)

Equate δek to (1/2)(m+m)v² to solve for v.

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posted by MathMate

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