1. Calculate the work done by a specified constant force on an object that undergoes a specified displacement.

2.  In physics, “work” is the product of the force on an object and the displacement through which the object is moved: force × displacement  We do work when we lift a load against Earth’s gravity. The heavier the load or the higher we lift it, the more work we do.

3. work = force × displacement W = Fd

4.  If we lift two boxes of equal mass, we do twice as much work as lifting one box the same distance because the force needed is twice as great.  If we lift one box twice as far, we do twice as much work because the distance is twice as great.

5.  Work is done in lifting the barbell. If the barbell could be lifted twice as high, the weight lifter would have to do twice as much work.

6.  While the weight lifter is holding a barbell over his head, he may get really tired, but he does no work on the barbell.  Only when the weight lifter raises the barbell is he doing work on it.

7.  Work is a scalar quantity – no direction.  When the force and the displacement are pointed in the same direction, work is positive.  When the force is pointed in the opposite direction of the displacement, work is negative.

8.  Every force acting on an object does work if the object moves (has a displacement). An archer stretches her bowstring – her pull does positive work while the elastic forces of the bow do negative work. When the ram of a pile driver is raised, the tension in the cable does positive work while gravity does negative work. When you do push-ups, the push from your arms does positive work on the way up and negative work on the way down while your weight does opposite work.  In each of these cases, the net work done is zero – positive work by one force (positive displacement), negative by the other (negative displacement).

9.  Since work is a force (newtons) times a displacement (meters), the units for work are newton-meters (N m )  One newton-meter is called 1 joule (1 J).  Work is usually expressed in joules.

10. FORCE ACCELERATION causes WORK acting for a distance is IMPULSE CHANGE IN MOMENTUM causes acting for a time is Newton’s 3 rd Law Conservation of Momentum

12. Which of the following is the correct definition of work (in algebraic terms)? A. W = ma/t B. W = Ft C. W = Fd D. W = Fp E. W = rk

13. In the metric system, what units are used to measure work? A. joules B. newton-meters C. kg-m 2 /s 2 D. All of the above. E. None of the above.

14. How much work is done by a force of +15 N acting over a displacement of +3.0 m? A. 0 J B. +5.0 J C. +12 J D. +18 J E. +45 J

15. How much force is needed to do 120 J of work over a displacement of 4.0 m? A. 0 N B. 30 N C. 116 N D. 124 N E. 480 N

16. When is work negative? A. When the force doing the work pushes to the left. B. When the displacement is to the left. C. When both the force and the displacement point left. D. When the force and displacement point in the same direction. E. When the force and displacement point in opposite directions.

17. A weightlifter lifts a 1000-N barbell by pushing upward with a force of 1000-N. If the barbell moves 2 m upward, what is the net work done on the barbell? A. -2000 J B. -500 J C. 0 J D. +500 J E. +2000 J