Springs, Power and Friction

Power Friction Springs

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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

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.

ANSWER:

•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.

ANSWER:

•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.

ANSWER:

•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.

ANSWER:

• 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.

ANSWER:

•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.

ANSWER:

•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.

ANSWER:

•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.

ANSWER:

•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.

ANSWER:

•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.

ANSWER:

•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.

ANSWER:

•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.

ANSWER:

•What is 89.4 N? (or -89.4 N if pulling down or left)

Springs – 40 Points

QUESTION:

•A bungee jumper of mass m = 50 kg falls 20 meters before the bungee stretches and 20 meters while it stretches. This is the bungee’s spring constant in N/m.

ANSWER:

•What is 98 N/m?

Springs – 50 Points

QUESTION:

•A bungee jumper of mass m = 75 kg falls 20 meters before her bungee (of k = 56 N/m) stretches. She stretches the bungee this far.

ANSWER:

•What is 24.3 m?