A person pushes a 11.4-kg shopping cart at a constant velocity for a distance of 27.1 m on a flat horizontal surface. She pushes in a direction 31.7 ° below the horizontal. A 47.2-N frictional force opposes the motion of the cart. (a) What is the magnitude of the force that the shopper exerts? Determine the work done by (b) the pushing force, (c) the frictional force, and (d) the gravitational force.

The answers need to be in Newtons or Joules.

b = 1278.65J

For (a), you'll need to know how to resolve forces into vertical and horizontal components.

First fact to consider, is that the cart is moving at a constant velocity. This means that the resultant force on the cart is ?

The horizontal component of the force applied by the shopper is thus ?

And from your knowledge of resolving forces, what would be the applied force?

(b) I think you have a little problem here... My calculator gives 47.2 x 27.1 = 1279.12 J

Even there, this is not good. Work is calculated from the net force. Since the speed of the cart is constant, there is no net force and the cart does not gain any kinetic energy, and by the principle of conservation of energy which you surely know, you cannot do work and this energy gets nowhere.

(c) & (d) what about you try these now, and tell what you think about them?

Post back what you got or ask if something bothers you in my post, even if you think that it's wrong, we'll try to help you understand :)