Complete Question:

A 10 kg block is pulled across a horizontal surface by a rope that is oriented at 60° relative to the horizontal surface.

The tension in the rope is constant and equal to 40 N as the block is pulled. What is the instantaneous power (in W) supplied by the tension in the rope if the block when the block is 5 m away from its starting point? The coefficient of kinetic friction between the block and the floor is 0.2 and you may assume that the block starting at rest.

Answer:

Power = 54.07 W

Explanation:

Mass of the block = 10 kg

Angle made with the horizontal, θ = 60°

Distance covered, d = 5 m

Tension in the rope, T = 40 N

Coefficient of kinetic friction, [tex]\mu = 0.2[/tex]

Let the Normal reaction = N

The weight of the block acting downwards = mg

The vertical resolution of the 40 N force, [tex]f_{y} = 40sin \theta[/tex]

[tex]\sum f(y) = 0[/tex]

[tex]N + 40 sin \theta – mg = 0\\N = -40sin60 + 10*9.81 = 0\\N = 63.46 N[/tex]

[tex]\sum f(x) = 0[/tex]

[tex]40 cos 60 – f_{r} – ma = 0\\ f_{r} = \mu N\\ f_{r} = 0.2 * 63.46\\ f_{r} = 12.69 N\\40cos 60 – 12.69-10a = 0\\7.31 = 10a\\a = 0.731 m/s^{2}[/tex]

[tex]v^{2} = u^{2} + 2as\\u = 0 m/s\\v^{2} = 2 * 0.731 * 5\\v^{2} = 7.31\\v = \sqrt{7.31} \\v = 2.704 m/s[/tex]

Power, [tex]P = Fvcos \theta[/tex]

[tex]P = 40 *2.704 cos60\\P = 54.074 W[/tex]