Unit 8 WS 4 NAME_____________________ per.___
1. Hulky and Bulky are two workers being considered for a job at the UPS loading dock. Hulky boasts that he can lift a 100 kg box 2.0 meters vertically, in 30 seconds. Bulky counters with his claim of lifting a 200 kg box 0.5 meters vertically, in 20 seconds. Calculate which worker has a greater power rating.
2. The trains on the Demon roller-coaster are raised from 10 m above ground at the loading platform to a height of 60 m at the top of the first hill in 45 s. Assume that the train (including passengers) has a mass of 800 kg. Ignoring frictional losses, what power motor would be required to accomplish this task?
3. A. A 3 kg ball is dropped from a height of 4 meters (assume no friction). How much time does this take? Show your work.
B. How much average power is provided by the Earth’s gravitational field to bring this ball to the ground?
4. Madison Gas & Electric charges by the kilowatt-hour. (This is Power in kilowatts x time in hours.) Does a utility company charge you for energy or power? Calculate how many Joules of energy are equal to 1 kilowatt-hour. (1 kilowatt =1000 watts)
5. Madison Gas and Electric has a 190 Megawatt power plant (1 megawatt = 106 watts).
A. How much energy does MG&E transfer to its customers in one day at this rate?
B. If 4.18 Joules = 1 calorie, how many calories is this? If a human needs 2,000,000 calories per day, how many days worth of energy is this for one human?
6. Ali can lift 32 kg at a constant speed of 0.5 m/s.
A) What is her change in Eg each second while lifting (in other words, what is her power)?
B) Ali’s little brother can lift 40 kg but his power is half as much as Ali’s. At what speed does he lift?
7. Ms. B. drives her 1200 kg Acura Integra along East Johnson Street at a constant 30 mi/hr. (13 m/s).
A) Compute the kinetic energy of the car. If she accelerates from rest to 13 m/s in 4 seconds, what is the car’s power?
B) One gallon of gas has ~131million Joules of chemical potential energy (Echem). If this car is 20% efficient, how much gas is used each time this 1200 kg car goes from 0 to 13 m/s? How much gas (in gallons) is used when the car goes from 0 to 26 m/s?
8. AT HOME: Find an electric appliance (other than a light bulb) at your residence that has a power rating in Watts printed on it (look on the back of the appliance). Answer the following:
A.) Type of appliance _______________________________
B.) Power rating ___________________________________
C.) According to the power rating, how many Joules of energy are used to run this appliance for 5 minutes? (Show calculations).
D.) If the above amount of energy was used to lift your own body straight up, how high could you be lifted? (1 kilogram = 2.2 pounds)
E.) If the above amount of energy were used to cause your own body to move, how fast would you be going?
9. Nick has a mass of 100 kg (220 lbs.) If he runs from Algebra II (1st floor) to physics in 14 seconds,
A. What is his power? (Each floor is 4 meters high.)
B. What are two measurements (quantities) that can be changed to improve his power while going up the stairs?
10. In the class activity where you timed yourself going up the stairs, what power did you calculate for yourself? Show your work.
A. My Power =
B. This power is equivalent to how many lit 100-Watt light bulbs?
C. With the same expenditure of energy as you did on the stairs, for how much time could you light one 100-watt bulb?