A boy pulls a 28.0-kg box with a 230-N force at 35° above a horizontal surface. If the coefficient of kinetic friction between the box and the horizontal surface is 0.24 and the box is pulled a distance of 30.0 m, what is the work done by the friction force on the box?

1977.696 J

Explanation:

Given;

Weight of the box = 28.0 kg

Force applied by the boy = 230 N

angle between the horizontal and the force = 35°

Therefore,

the horizontal component of the force = 230 * cosθ

= 230 * cos 35°

= 188.405 N

Coefficient of kinetic friction, μ = 0.24

Force by friction, f = μN

here,

N = Normal force = Mass * acceleration due to gravity

or

N = 28 * 9.81 = 274.68 N

therefore,

f = 0.24 * 274.68

or

f = 65.9232 N

Now,

work done by the boy, W₁ = 188.405 N * Displacement

= 188.405 N * 30

= 5652.15 J

and,

the

work done by the friction, W₂ = - 65.9232 N * Displacement

= - 65.9232 N * 30 m

= - 1977.696 J

[ since the friction force acts opposite to the direction of motion, therefore the workdone will be negative]