Concept #1: Calculating Net Work
Practice: A 3-kg box is on a flat surface. The box-floor coefficient of friction is 0.6. When you pull horizontally on it for 10 m, it moves with 2 m/s2 . Find the net work on the box. (Start by finding the magnitude of all forces acting on the box)
Practice: A 2-kg box is on a rough horizontal surface. When you pull horizontally on it, it moves with 3 m/s2 . The magnitude of your force and the box-floor coefficient of friction are unknown. What is the net work on the box across 5 m?
Concept #2: The Work-Energy Theorem
Practice: A 4-kg object has speed 6 m/s at point A, and speed 10 m/s at point B.
(a) How much work was done to it between A and B?
(b) If –32 J of total energy is done to the object between B and C, what speed does it have at C?
Concept #3: The Work-Energy Theorem,ually
Practice: You lift a 3 kg object from the floor to a height of 2 m. Find the:
(a) work done by you;
(b) work done by gravity;
(c) net work done on the object. You then walk horizontally with the object for 10 m.
(d) How much work do you do?