CHAPTER 6 COPY ALL INFO IN THE BLACK FONT Work and Power Notes Nov 5

Work Work = Force x distance In science, work is a form of energy you either use or get when a force is applied over a distance.  Holding a heavy box stationary does not result in work being done on the box, even though biological work is being done.  The unit of work is the joule (J). This results from N∙m

You do 1 joule of work if you push with a force of 1 newton for a distance of 1 meter joules equals a Calorie. Work is done by forces that cause movement. * Work is done on objects. * If nothing moves (distance is zero), then no work is done. Doing work always means transferring energy.

1.How much work is done to lift a 500 N box to a height of 4 m? 2.A person performs 420,000J of work on a stroller to push it 1600m. How much force was exerted on the stroller to do this? 3.A box is slid across the floor by a force of 25N. This required 125J of work. How far did the box go? 4.A person holds a heavy box in their arms. The box does not move. How much work is done on the box? Practice Problems

Power Power = work ÷ time The rate at which work is done is called Power. It makes a difference how quickly the work is done! The unit of power is the Watt (W) = J/s Lifting an object quickly is more difficult than lifting it slowly. One horsepower still equals 746 watts.

Michael and Jim do the same amount of work. Jim’s power is greater because he gets the work done in less time. Who did more biological work?

Practice Problems 5. If one lifts a 5 kg bowling ball 1 meter it takes 50 J of work regardless of how fast they lift the ball. How much power does it take to lift the ball in 1 sec? How much power does it take to lift the ball in 5 sec?

6. Allen lifts his weight (500 newtons) up a staircase that is 5 meters high in 30 seconds. How much power does he use? How does his power compare with a 100-watt light bulb?

7. Jane moves a box 10 meters in 4s and exerts a force of 100N. Jack moves a similar box 10m also with a force of 100N, but it takes him 9s. How much power do they both use? 8. A light bulb with a power of 100W burns for 30min (1800s). How much work was done by the electricity in this light bulb?

Weight g = gravity = 9.8m/s/s