Block A as shown in Fig weighs `2.0 N` and block B weighs `6.0 N` The coefficient of ikinetic friction between all surface is `0.25` Find the magnitude of the horizontal force necessary to drag block B to the left at constant speed if A and B are connected by a light , flxeible cord passing around a fixed, frictionless pulley

Options

A. `2 N`
B. `3N`
C. `5N`
D. `6 N`

Answer

b

Explanation

The friction force on block A is `mu_(s)w_(A) = (0.25)(2 N) = 0.5 N` This is the roagnitade of the friction that block A exerts on block B as well as the tension in the string The force F must then have magnitude
`F = mu_(k) (w_(B) + w_(A)) + mu_(k) w_(A) +T `
`= mu_(k) (w_(B) + 3w_(A)) = (0.25)(6N+ 3)(2N))=3 N`
note that the normal force exerted on block B by the table the sum of the weight of the blocks