Question

On a Saturday afternoon, you decide to pay a neighborhood kid to mow your lawn. The kid is using a manual push lawn mower with a mass of 12 kg. The handle of the lawnmower is tilted 37 degrees above the horizontal and the coefficient of kinetic friction between the lawnmower and the ground is 0.16. How much power does the kid supply to the lawnmower if the lawnmower is moving at a constant speed of 1.5 m/s? Assume the kid is pushing parallel to the handle.

Answer 1

here,

mass , m = 12 kg

theta = 37 degree

the coefficient of kinetic friction , uk = 0.16

constant speed , v = 1.5 m/s

let the force applied by the kid be F

equating the forces vertically

m * g - F * sin(theta) = N

so, for constant speed

the net force in horiontal direction is zero

uk * N = F * cos(theta)

uk * (m * g - F * sin(theta)) = F * cos(theta)

0.16 * ( 12 * 9.81 - F * sin(37)) = F * cos(37)

solving for F

F = 21.05 N

the power applied by the kid , P = F * v * cos(37)

P = 21.05 * 1.5 * cos(37) W = 25.2 W