Physics help please

Question

A 9-kg sled sliding freely on an icy surface experiences a 3-N frictional force exerted by the ice and an air-resistive force of 0.6 N.

1. What is the net force acting on the sled?  Links to an external site.
2. What is the acceleration of the sled? 

Answer 1

Hello Maya,

The net force is the vector sum of all described forces being exerted on the sled. Since the sled is "sliding freely" the presumed occupant of the sled is not actively propelling the sled in any direction. The only described forces are the surface frictional force and the air-resistive force. Both of these forces are exerted in the same direction, that is, in the opposite direction of the sled's velocity. Thus we add these forces together: 3.6 N

(note: since the force is opposite of the direction of velocity, the answer could very well be -3.6 N)

The acceleration of the sled necessitates the formula:

F = ma = 3.6 N

The problem describes the mass as equal to 9kg, so:

3.6 = 9 * a

Solving for "a" gives: 0.4 m/s²