A father gives his sons a ride by pulling a sled across the rough snow, as shown

Question

A father gives his sons a ride by pulling a sled across the rough snow, as shown. The father runs across the snow with a constant acceleration 'a' while pulling the sled at T = 140 N, at 40° above the horizontal. The combined mass of the sled and sons is 50.0 kg. The coefficient of kinetic friction between the sled and the snow is 0.150. Draw a free-body diagram and determine the following:

a. What is the magnitude of the kinetic frictional force exerted by the ground on the sled?

b. What is the magnitude of the acceleration of the children and sled?

Explanation / Answer

a) sum of Fx: -fk + 140cos40 = max

sum of Fy: n-mg +140sin40 = may

sum Fx: 140cos40 - 0.150 = max
sum Fy: n-mg + 140 sin40 = 0
n = mg - 140*sin40
n = (50*9.8) - 140sin40  = 400 N

b) a = (140 cos40 - 0.150) /50kg  = 2.14 m/s^2

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