A block of mass m = 3.20 Times 10^2 g is dragged with a string across a rough ho

Question

A block of mass m = 3.20 Times 10^2 g is dragged with a string across a rough horizontal table. The string tension is T = 3.59 N, and it pulls upward at an angle of (p = 44.0 degree with the horizontal. At one particular instant the block is moving at a speed of v = 6.70 m/s. The coefficient of kinetic friction between the block and the table is mu_k = 0.669. What is the power supplied to the block by the string tension? What is the power supplied by the force of friction? At this instant the block's speed is decreasing. constant. increasing. impossible to determine.

Explanation / Answer

a)   power supplied to block by string tension = T.v    =   T * v * cos(theta)

                                                                       = 3.59 * 6.70 * cos44

                                                                         = 17.302 W

b)     Here, Normal Force = 0.32 * 9.8 - 3.59 * sin44

                                           = 0.642 N

=> force of friction =   0.669 * 0.642   =   0.429 N

=> power supplied by force of friction = - 0.429 * 6.70 = - 2.874 W

c)   Block's speed is increasing .

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