MEDAL GIVEN TO CORRECT ANSWER.
Jake drags a sled of mass 10 kg across the snow. The sled is attached to a rope that he pulls with a force of 30 N at an angle of 25°. If there is no friction, what is the normal force acting on the sled?

A. 27.2 N
B. 70.8 N
C. 85.3 N
D. 12.7 N

Question

MEDAL GIVEN TO CORRECT ANSWER. 
Jake drags a sled of mass 10 kg across the snow. The sled is attached to a rope that he pulls with a force of 30 N at an angle of 25°. If there is no friction, what is the normal force acting on the sled?

 		A.	27.2 N
 		B.	70.8 N
 		C.	85.3 N
 		D.	12.7 N

anonymous · Answer

Princess,

If the 30 N on the rope were pulled straight up, it would offset the force of gravity ( m g = 10 kg * 9.8 N/kg = 98 N) , leaving a net force up from the ground on the sled of 98-30 = 68 N. Since the rope is pulled at the angle of 25o, only part of the force is in the upward direction, (30N)(sin(25) = (30)(.423) = 12.7.

So the net force becomes 98 N down offset by 12.7 up or
98-12.7 = 85.3 N. Ah, there it is: C.