ࡱ> BDAM bjbj== 0WWlDDDDDDDX    & ,Xd*^ ^ ^ ^ ^ ^ ^ ^ )))))))$+ :-V *D^ ^ ^ ^ ^ *2DD^ ^ *222^ D^ D^ )2^ )22/(DD)^ R AX   &()4*0d*(.6.)2XXDDDDInstructors Copy Worksheet: Work & Power Problems I. Work A. Sample Problems: 1. F = 200 Newtons Formula: W = Fd d = 50 meters Substitution: W = (200 N)(50 m) W = ? Answer with unit of measure: W = 10,000 J 2. F = 5 Newtons Formula: d = W/F W = 75 Joules Substitution: d = 75 J/5 N d = ? Answer with unit of measure: d = 15 m 3. W = 125 Joules Formula: F = W/d d = 10 meters Substitution: F = 125 J/10 m F = ? Answer with unit of measure: F = 12.5 N If 150 Joules of work is needed to move a box 10 meters, what force was used? W = 150 J F = W/d F = 15 N d = 10 m F = 150 J/10 m B. Fill-in-the-blank: 1. Work is done when an object moves through a distance because of a force acting upon the object. 2. When calculating work, you should use the formula: work = force X distance. 3. The SI unit for work is the Joule. It is represented by the letter J. C. Work Problems: F = 90 N W=Fd 5. F = 6 N d=W/F 6. W = 120 J F=W/d d = 5 m 90(5) W = 72 J 72/6 d = 24 m 120/24 W = ? 450 J d = ? 12 m F = ? 5 N W = ? W = Fd 8. W = 13.2 J d = W/F 9. W = 136 J F = W/d F = 62.6 N 62.6(13) F = 2 N 13.2/2 d = 27.2 m 136/27.2 d = 13 m 813.8 J d = ? 6.6 m F = ? 5 N 10. If 360 Joules of work are needed to move a crate a distance of 4 meters, what is the weight of the crate? W = 360 J F = W/d F = 90 N d = 4 m F = 360 J/4 m 11. If a group of workers can apply a force of 1000 Newtons to move a crate 20 meters, what amount of work will they have accomplished? F = 1000 N W = Fd W = 20,000 J d = 20 m W = 1000(20) 12. If 68 Joules of work were necessary to move a 4 Newton crate, how far was the crate moved? W = 68 J d = W/F d = 17 m F = 4 N d = 68 J/4N 13. How much work is done in holding a 15 N sack of potatoes while waiting in line at the grocery store for 3 minutes. Not moving F = 15 N W = Fd W = 0 J d = 0 m W = 15(0) II. Power A. Samples 1. W= 500 Joules Formula: P = W/t t = 25 seconds Substitution: P = 500 J/25 sec P = ? Answer with unit of measure: 20 W 2. P = 25 watts Formula: t = W/P W = 5000 Joules Substitution: t = 5000 J/25 W t = ? Answer with unit of measure: t = 200 sec 3. P = 170 watts Formula: W = Pt t = 20 seconds Substitution: W = 170 W(20 sec) W = ? Answer with unit of measure: W = 3,400 J 4. If a man moves a large box that weighs 10 Newtons 20 meters in 30 seconds, how much power was used? F = 10 N P = W/t and W = Fd, so P = Fd/t d = 20 m P = (10 N x 20 m)/30 sec t = 30 sec P = 6.67 W B. Fill-in-the-blank: 1. Power is the rate at which work is done. When calculating power, you should use the formula P = work divided by time. In this formula, P stands for power, W stands for work, and t for time. The SI unit for Power is the Watt. C. Power Problems W = 100 J P = W/t 5. W = 225 J t = W/P 6. P = 20 W W = Pt t = 10 s P = 100/10 P = 25 W t = 225/25 t = 15 s W = 20 x 15 P = ? P = 10 W t = ? t = 9 sec W = ? W = 300 J W = 500 J P = W/t 8. W = 336 J t = W/P 9. W = ? W = Pt t = 25 s P = 500/25 t = ? t = 336/14 t = 16.6 s W = 64(16.6) P = ? P = 20 W P = 14 W t = 24 sec P = 64 W W = 1,062.4 J 10. A person weighing 600 N gets on an elevator. The elevator lifts the person 6 m in 10 seconds. How much power was used? F = 600 N P = Fd/t d = 6m P = (600 x 6)/10 t = 10 sec P = 360 W 11. How much time is needed to produce 720 Joules of work if 90 watts of power is used? W = 720 J t = W/P t = 8 sec P = 90 W t = 720 J/90 W 12. If 68 W of power is produced in 18 seconds, how much work is done? P = 68 W W = Pt W = 1,224 J t = 18 sec W = 68(18) 13. A set of pulleys lifts an 800 N 4 meters in 7 seconds. What power was used? 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