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?

 

[m2003]

I can confirm that your calculation for the normal force is correct. The normal force is always perpendicular to the surface and therefore acts in the opposite direction of the force of gravity. So in this case, the normal force would be positive (509.6 N) and the force of gravity would be negative (-509.6 N).

To convert Newtons (N) into Joules (J), you would need to know the distance over which the force is applied, as work is equal to force multiplied by the distance traveled. In this case, since the box is pushed 7.0 meters, you would multiply the force (149 N) by the distance (7.0 m) to get the work done, which would be 1043 J.