January 07, 2015
Chapter 5 Work and Energy
Grade: «grade» Subject: «subject» Date: Jan 10, 2012
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Section 51 Work Pg 170 Work
1. A tugboat pulls a ship with a constant net horizontal force of 5000 N and causes the ship to move through a harbor. How much work is done on the ship if it moves a distance of 3.00 km?
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2. A weight lifter lifts a set of weights a vertical distance of 2.00 m. If a constant net force of 350 N is exerted on the weights, what is the net work done on the weights?
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3. A shopper in a supermarket pushes a cart with a force of 35 N directed at an angle of 25° downward from the horizontal. Find the work done by the shopper on the cart as the shopper moves along a 50.0 m length of aisle.
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4. If 2.0 J of work is done in raising a 180 g apple, how far is it lifted?
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Section 52 Energy Pg 174 Kinetic energy
1 1. Calculate the speed of an 8.0 x 104 kg airliner with a kinetic energy of 1.1x 109J.
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2. What is the speed of a 0.145 kg baseball if its kinetic energy is 109 J?
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2 3. Two bullets have masses of 3 g and 6 g, respectively. Both are fired with a speed of 40 m/s. A
Which bullet has more kinetic energy?
B
What is the ratio of their kinetic energies?
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4. Two 3.0 g bullets are fired with speeds of 40.0 m/s and 80.0 m/s, respectively. A What are their kinetic energies?
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B Which bullet has more kinetic energy?
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C What is the ratio of their kinetic energies?
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5. A car has a kinetic energy of 4.32 x 105 J when traveling at a speed of 23 m/s. What is its mass?
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Pg 176 WorkKinetic Energy Theorem
1. A student wearing frictionless inline skates on a horizontal surface is pushed by a friend with a constant force of 45 N. How far must the student be pushed, starting from rest, so that her final kinetic energy is 352 J?
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2. A 2000 kg car accelerates from rest under the actions of two forces. One is a forward force of 1140 N provided by traction between the wheels and the road. The other is a 950 N resistive force due to various frictional forces. Use the work—kinetic energy theorem to determine how far the car must travel for its speed to reach 2.0 m/s.
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3. A 2100 kg car starts from rest at the top of a driveway that is sloped at an angle of 20.0° with the horizontal. An average friction force of 4000 N impedes the car’s motion so that the car’s speed at the bottom of the driveway is 3.8 m/s. What is the length of the driveway?
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4. A 75 kg bobsled is pushed along a horizontal surface by two athletes. After the bobsled is pushed a distance of 4.5 m starting from rest, its speed is 6.0 m/s. Find the magnitude of the net force on the bobsled.
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3 5. A 10.0 kg crate is pulled up a rough incline with an initial speed of 1.5 m/s.The pulling force is 100.0 N parallel to the incline, which makes an angle of 150 with the horizontal. Assuming the coefficient of kinetic friction is 0.40 and the crate is pulled a distance of 7.5 m, find the following: A the work done by the Earth’s gravity on the crate B the work done by the force of friction on the crate
C the work done by the puller on the crate
D the change in kinetic energy of the crate E the speed of the crate after it is pulled 7.5 m
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Pg 180 Potential energy
4 1. A spring with a force constant of 5.2 N/m has a relaxed length of 2.45 m. When a mass is attached to the end of the spring and allowed to come to rest, the vertical length of the spring is 3.57 m. Calculate the elastic potential energy stored in the spring.
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5 2. The staples inside a stapler are kept in place by a spring with a relaxed length of 0.115 m. If the spring constant is 51.0 N/m, how much elastic potential energy is stored in the spring when its length is 0.150 m?
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3. A 40 kg child is in a swing that is attached to ropes 2 m long. Find the gravitational potential energy associated with the child relative to the child’s lowest position under the following conditions:
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Section 53 Conservation of Energy Pg 185 Conservation of Mechanical energy
6 1. A bird is flying with a speed of 18.0 m/s over water when it accidentally drops a 2.00 kg fish. If the altitude of the bird is 5.40 m and friction is disregarded, what is the speed of the fish when it hits the water?
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7 2. A 755 N diver drops from a board 10.0 m above the water’s surface. A Find the diver’s speed 5.00 m above the water’s surface.
B
Then find the diver’s speed just before striking the water.
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8 3. If the diver in item 2 leaves the board with an initial upward speed of 2.00 m/s, find the diver’s speed when striking the water.
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9 4. An Olympic runner leaps over a hurdle. If the runner’s initial vertical speed is 2.2 m/s, how much will the runner’s center of mass be raised during the jump?
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10 5. A pendulum bob is released from some initial height such that the speed of the bob at the bottom of the swing is 1.9 m/s. What is the initial height of the bob?
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Section 54 Power Pg 189 Power
11 1. A 1000 kg elevator carries a maximum load of 800.0 kg. A constant frictional force of 4000 N retards the elevator’s motion upward. What minimum power, in kilowatts, must the motor deliver to lift the fully loaded elevator at a constant speed of 3.00 m/s?
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12 2. A car with a mass of 1500 kg starts from rest and accelerates to a speed of 18.0 m/s in 12.0 s. Assume that the force of resistance remains constant at 400.0 N during this time. What is the average power developed by the car’s engine?
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13 3. A rain cloud contains 2.66 x 107 kg of water vapor. How long would it take for a 2.00 kW pump to raise the same amount of water to the cloud’s altitude, 2.00 km?
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14 4. How long does it take a 19 kW steam engine to do 6.8 x 107 J of work?
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15 5. A 1500 kg car accelerates uniformly from rest to 10.0 m/s in 3.00 s. A
B
What is the work done on the car in this time interval?
What is the power delivered by the engine in this time interval?
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