You're using a rope to pull a sled at constant velocity across level snow, with coefficient of kinetic friction 0.050 between sled and the snow. The sled is loaded with physics books, giving a total mass of 39 kg
1. With what force should you pull with the rope horizontal?
2. Repeat for the rope at 30

Explanation:

Frictional force acting on the sled = μ mg , μ is coefficient of friction , m is mass of the load .

Frictional force acting on the sled = .05 x 39 x 9.8

= 19.11 N

So a horizontal force  of 19.11 N is required to pull the rope so that it moves with uniform velocity .( net force zero so no acceleration )

When force acts at an angle of 30 degree

The horizontal component will be effective to pull the load and reaction force will be reduced

reaction force = mg - Fsin30

= 39 x 9.8 - F/2

frictional force = .05 ( 39 x 9.8 - F/2 )

F cos 30 = .05 ( 39 x 9.8 - F/2 )

.866 F + .025F = 19.11

F = 19.11 / .891

= 21.44 N .