A horizontal force of 20 N drags a small sled 42 m across the ice at constant speed. Find the work done by the pulling force and the friction force. What is the resultant force?

If the speed of a small sled is always constant, then this means that acceleration a = 0 m/s^2.

From F = m*a it follows that the resulting force F is m*0, which is also 0. Hence, pulling force is equal to the friction force in the magnitude. However, they are opposite in the direction.

m*0 = F(res.) = F(pull) + F(friction) = 0

F(pull) = - F(friction) = 20N. Forces are equal in magnitude and therefore, the work they have done is also equal in absolute value.

Work by a force W = F*s.