Write Definitions for: Work & Power Write Definitions for: Work Power

In Terms of Physics, What is Happening Here?

Work Work is done when there is movement against an opposing force.

e.g. John took 5 s to run 200 m. Calculate his speed. How to do calculations e.g. John took 5 s to run 200 m. Calculate his speed. time = 5 s distance = 200 m Write down the information given Decide which formula to use and write it down Put the values into the formula Calculate your answer Add units!!! speed = distance / time speed = 200 / 5 speed = 40 speed = 40 m/s

Calculating Work Done Work done = force x distance moved (J) (N) (m) What is work done on an object if a force of 300 N moves it 8 m? How much work is done if an object weighing 900 N is moved up 100 m by a crane?

Question 1 What is work done on an object if a force of 300 N moves it 8 m? Work done = force x distance moved Work = 300 x 8 Work = 2400 J

Question 2 How much work is done if an object weighing 900 N is moved up 100 m by a crane? Work done = force x distance moved Work done = 900 x 100 Work = 90 000 J Work = 90 kJ

Which car has the most power?

Which car has the most power? WRONG!!!! This is not the Physics definition of power.

Which car has the most power? Same weight. Same hill. Same amount of work.

Power Power = work done time taken Power = watt (W)

Questions A cat who weighs 40 N climbs a tree that is 15 m tall in 10 s. Calculate the work done by the cat and the cat’s power. Oliver weighs 600 N. He climbs a flight of stairs that is 3.0 m tall in 4.0 seconds. What was Oliver’s power in watts?

Work done = Force x Distance Questions A cat who weighs 40 N climbs a tree that is 15 m tall in 10 s. Calculate the work done by the cat and the cat’s power. Work done = Force x Distance Work done = 40 x 15 = 600 J Power = Work done/time Power = 600 / 10 = 60 W

Questions 2. Oliver weighs 600 N. He climbs a flight of stairs that is 3.0 m tall in 4.0 seconds. What was Oliver’s power in watts? Work done = Force x Distance Work done = 600 x 3.0 = 1 800 J Power = Work done/time Power = 1 800 / 4.0 = 450 W

Relay Race Work in pairs. Collect a question from your envelope at the front of the room. Answer the question. Return the question and collect another one. Rules Only 1 Q from the envelope at a time. Must return a Q before collecting another one. No running.

Red for Fred, Blue for Stu Fred is hoisting a 2 kg bucket of water out of a well 5 m out of a well. Stu pushes a trolley of three of these buckets up a small slope 2 m high.

Red for Fred, Blue for Stu Fred is hoisting a 2 N bucket of water out of a well 5 m out of a well. Work = force x distance = 2 x 5 = 10 J Stu pushes a trolley of three of these buckets up a small slope 2 m high. Work = force x distance = (3 x 2) x 2 = 12 J

Red for Fred, Blue for Stu Fred does this 2 times every minute Stu has to wait for Fred to pass him the bucket and so does this once every minute and a half. Who has more power?

Red for Fred, Blue for Stu Fred does this 2 times every minute Power = work / time = 20 / 60 = 0.3 W Stu has to wait for Fred to pass him the bucket and so does this once every minute and a half. Power = work / time = 12 / 90 = 0.13 W

Red for Fred, Blue for Stu After work Fred and Stu go to the gym. Fred lifts 40 kg weights 50 cm (although we should call them masses!) once in each hand taking 30 s each time. Stu lifts 7 kg weights 50 cm 10 times in each hand, taking 2 s each time. Who has more power? Hint: 1 kg = 10 N

Red for Fred, Blue for Stu Fred lifts 40 kg weights 50 cm (although we should call them masses!) once in each hand taking 30 s each time. Work = force x distance = 400 x 0.5 x 2=400J Power = work / time = 400 / 60 = 6.7 W Stu lifts 7 kg weights 50 cm 10 times in each hand, taking 2 s each lift. Work = force x distance = 70 x 0.5 x 10 = 350 J Power = work / time = 350 / 40 = 8.75 W