Block A in the figure weighs 1.80N and block B weighs 3.80N . The coefficient of

Question

Block A in the figure weighs 1.80N and block B weighs 3.80N . The coefficient of kinetic friction between all surfaces is 0.500

1)Find the magnitude of the horizontal force F? a necessary to drag block B to the left at a constant speed of 9.50cm/s if A  rests on B  and moves with it (figure a).

2)Find the magnitude of the horizontal force F? b necessary to drag block B to the left at a constant speed of 9.50cm/s if A  is held at rest by a string (figure b).

3)In part (A), what is the friction force on block A?

Explanation / Answer

1)

LEt the Force be F

So, wirting the equation of motion :

F - u*mg = 0 <---- net force = 0 as it moves with constant speed

where m = m1 + m2

So, F = umg

So, F = 0.5*(1.8+3.8) = 2.8 N <------answer

2)

Writing the equation of motion of block B:

F - u*(m1+m2)*g - u*(m1*g) = 0

So, F = u*(2*m1*g + m2*g)

So, F = 0.5*(2*1.8 + 3.8) = 3.7 N <------answer

3)

friction force on A = m1*a

where a = acceleration of mass = 0

So, friction on A = 0 <--------answre

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