Find the Force of friction

Question

The person and the sled have a weight of

1500 N. The dogs must exert a combined

horizontal force of 300 N to pull the sled

at constant velocity. Find the normal

force and the force of friction on the sled.

Answer 1

The normal force is equal and opposite to the weight of the person and sled:

W = N

W = 1500N down

=> N = 1500 N straight up

F_dogs = 300N horizontally for constant velocity (a = 0)

Sum the forces in the horizontal direction:

ΣF = ma but remember a = 0, so

ΣF = 0

Horizontal forces: F_dogs ; F_friction

ΣF = F_dogs - F_friction = 0

F_dogs - F_friction = 0

=> F_dogs = F_friction = 300N opposite the motion