Springs, Power and Friction

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Springs, Power and Friction - PowerPoint PPT Presentation

Springs, Power and Friction. Power. Friction. Springs. 10. 10. 10. 20. 20. 20. 30. 30. 30. 40. 40. 40. 50. 50. 50. Power – 10 Points. QUESTION: Your toaster uses 7200 Joules every hour and therefore has this power in Watts. ANSWER: What is 2 W?. Power – 20 Points.

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Presentation Transcript

Power

Friction

Springs

10

10

10

20

20

20

30

30

30

40

40

40

50

50

50

Power – 10 Points
• QUESTION:
• Your toaster uses 7200 Joules every hour and therefore has this power in Watts.
• What is 2 W?
Power – 20 Points
• QUESTION:
• You have four 50 W lightbulbs in your room. You study with them on for 2 hours a day for one week and use this much energy in kWh.
• What is 2.8 kWh?
Power – 30 Points
• QUESTION:
• You want to lift a 900 kg elevator up 30 stories (120 m). The elevator needs to ascend at a rate of 5 seconds per story. You buy a motor with this many Watts of power.
• What is 7056 W?
Power – 40 Points
• QUESTION:
• Your 1200 kg car is travelling 10 m/s and uses friction to stop over 5 s. Thermal energy is generated in this process with this power.
• What is 12000 W?
Power – 50 Points
• QUESTION:
• You find a 10 m high waterfall where 1000 kg of water flow over it every second. If you set up a turbine to convert the water’s KE at the bottom of the waterfall into electricity, your turbine produces enough power to light this many 100-W lightbulbs.
• What is 980 lightbulbs?
Friction – 10 Points
• QUESTION:
• Your 1000 kg car is travelling 5 m/s and then uses friction to stop. Friction did this much work in J.
• What is - 12500 J?
Friction – 20 Points
• QUESTION:
• A 500 kg rollercoaster starts off on an 80 m high hill. If friction does -100,000 J of work between the first hill and the second, the second hill must be this high.
• What is 60 m?
Friction – 30 Points
• QUESTION:
• A cross-country skier crosses a patch of snow with coefficient of friction = 0.1. If she starts off going 10 m/s, she travels this far along the snow before friction stops her.
• What is 51 m?
Friction – 40 Points
• QUESTION:
• A 10-m tall grassy hill has a coefficient of friction of 0.15 and a slope of 30 degrees. A box moves this fast at the bottom of this hill.
• What is 12.0 m/s?
Friction – 50 Points
• QUESTION:
• A 10 m tall grassy hill has a coefficient of friction of 0.12. If a box is moving 10 m/s at the bottom of the hill, the hill has this slope.
• What is 13.8 degrees?
Springs – 10 Points
• QUESTION:
• A spring of spring constant k = 100 N/m is stretched 0.1 m. The spring stores this much spring potential energy.
• What is 0.5 J?
Springs – 20 Points
• QUESTION:
• To store 50 J of PEs, a spring with spring constant k = 150 N/m is stretched this far.
• What is 0.82 m?
Springs – 30 Points
• QUESTION:
• A spring with spring constant k = 40 N/m stores 100 J of energy. At that point, the spring pulls back with this much force in N.