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COCHISE COLLEGE
PHYSICS HOMEWORK ASSIGNMENT A-13
POWER AND ENERGY
VALUE: 60 Points
Due Date:
1.
If 270.0 m3 of water goes over a waterfall 53.0 m high every minute.
(a) Calculate the power released in watts.
(b) Convert this power to kilowatts.
(c) Calculate how many kilowatthours of energy are released in one year.
(d) If 50% of the power is extracted by turbine engines and converted to electrical
energy, calculate the value of the energy generated in one year (in dollars) if one
kilowatt.hour is worth 9 cents.
2.
A 4.60 kg bowling ball is suspended from the ceiling as a simple pendulum by a cable.
If the pendulum is 6.00 m long and is pulled back until the cable makes an angle of 42
with the vertical, calculate:
(a) the potential energy of the bowling ball
(b) the maximum kinetic energy that it will develop
(c) the velocity of the bowling ball at the bottom of its swing.
3.
An elevator and cable of mass 2600 kg contains a group of people of mass 500kg.
An electric motor of 30% efficiency operates the elevator. (70% of the incoming
electrical energy is lost in friction and heat.)
If electrical energy costs the hotel 11 cents per kilowatthour, how much electrical
energy in dollars does it take to move the elevator and its load up 32 floors? Assume
that one floor equals 3.50 meters.
(Calculate the work done in joules and then convert to kilowatthrs.)
4.
An electric motor draws ½ horsepower while it is operating. The motor is used
continuously for 12 hours a day to run an evaporative cooler. Assume that electrical
energy costs 11 cents per kilowatthour.
(a) What is the electrical cost for a 12 hour period?
(b)If 12 hours per day is the normal average for summer use, then how much does
running the evaporative cooler add to a typical electric bill for a month (30 days)?
5.
Using the concept of conversion of potential energy to kinetic energy, calculate the
speed of a pendulum bob hanging from a 70.0 m rope that has been deflected 14
from a vertical position and then released..
Calculate the speed (a) in m/s and (b) mi/hr.
6.
If a football player of weight 220 lbs can carry a sack of concrete of weight 90 lbs up 3
flights of stair (30 ft total) in 18.0 sec, how much power in horsepower is he putting
out?