How Do You Calculate Normal Force and Work Done in Physics Problems?

[LostInScience]

52 kg box is pushed 7.0 meters by a force with a magnitude of 149 N. The coefficient of kinetic friction is 0.25. Determine normal force, force of gravity and frictional force.

For the normal force I have 52 * 9.8 = 509.6 N Which is also the the force of gravity. However which is positive and which is negative? I assume normal force is positive since it pushes up against gravity pushing downward? Also, how would I convert Newtons into Joules?

 

[PhanthomJay]

52 kg box is pushed 7.0 meters by a force with a magnitude of 149 N. The coefficient of kinetic friction is 0.25. Determine normal force, force of gravity and frictional force.

For the normal force I have 52 * 9.8 = 509.6 N Which is also the the force of gravity. However which is positive and which is negative? I assume normal force is positive since it pushes up against gravity pushing downward? Also, how would I convert Newtons into Joules?

As long as you are consistent, it doesn't matter which direction is positive or negative. Generally, down is usually taken as negative. Now don't confuse Newtons, a unit of force, with Joules, a unit of energy or work. How much work does each force do on the box?