Physics 011

MC#6A

Chapter 6: Work and Energy

1.	How much work is done when a 0.50-kg mass is pushed by a 20-N force through a distance of 10.0 meters? (Assume the force is parallel to the displacement.) The correct answer: 200 J See Section 6-1
2.	The derived unit for energy and work is called the joule, J. It is equivalent to which combination of SI units? The correct answer: kg m^2/s^2
3.	Work is done when a force I. acts vertically on a box moving along a horizontal surface. II. exerted on one end of a box is equal and opposite to a force exerted on the other end of the box. III. pushes a box up a frictionless incline. IV. of gravitational attraction acts between a box and the surface of the earth.
4.	If the velocity of a body is doubled, its kinetic energy The correct answer: increases to four times its original value. See Section 6-3
5.	What is the kinetic energy of a 10.0-kg mass with a velocity of 2.00 m/s? The correct answer: 20 J See Section 6-3
6.	Cart A has a mass of 1 kg and a constant velocity of 3 m/s. Cart B has a mass of 1.5 kg and a constant velocity of 2 m/s. Which statement is true? The correct answer: Cart A has the greater kinetic energy.
7.	If the speed at which a car is traveling is tripled, by what factor does its kinetic energy increase? The correct answer: 9 See Section 6-3
8.	Work is measured in the same units as The correct answer: energy. See Section 6-3
9.	What happens to the speed of a body if its kinetic energy is doubled? The correct answer: It is multiplied by 2^1/2. See Section 6-3
10.	An object of mass mo is initially at rest on a horizontal, frictionless surface. The object is then subjected to a constant force of magnitude Fo which makes an angle o with the horizontal as in the figure at the right. After the object has undergone a horizontal change in displacement Do, it has speed vo and kinetic energy KEo. If the angle which the force makes with the horizontal had been slightly less than o, the speed of the object after the horizontal change in displacement Do would have been __________ vo. The correct answer: more than
11.	An object of mass mo is initially at rest on a horizontal, frictionless surface. The object is then subjected to a constant force of magnitude Fo which makes an angle o with the horizontal as in the figure at the right. After the object has undergone a horizontal change in displacement Do, it has speed vo and kinetic energy KEo. If the mass of the object had been slightly more than mo, the kinetic energy of the object after the horizontal change in displacement Do would have been __________ KEo. The correct answer: equal to See Section 6-1, 6-3
12.	An object of mass mo is initially at rest on a horizontal, frictionless surface. The object is then subjected to a constant force of magnitude Fo which makes an angle o with the horizontal as in the figure at the right. After the object has undergone a horizontal change in displacement Do, it has speed vo and kinetic energy KEo. If the horizontal change in displacement had been 2 Do, the kinetic energy of the object after this horizontal change in displacement would have been KE = KEo x __________. The correct answer: 2 See Section 6-3
13.	An object of mass mo is initially at rest on a horizontal, frictionless surface. The object is then subjected to a constant force of magnitude Fo which makes an angle o with the horizontal as in the figure at the right. After the object has undergone a horizontal change in displacement Do, it has speed vo and kinetic energy KEo. If the same force continued to act on the object until the speed of the object was 2 vo, the total distance through which the force would have acted would be Do x ___________. The correct answer: 4 See Section 6-3
14.	If the work required to get an object with mass mo initially at rest to a speed vo is Wo, . . . . . . the additional work required to increase its speed from vo to 2 vo would be W o x ____________. The correct answer: 3 See Section 6-3
15.	If the work required to get an object with mass mo initially at rest to a speed vo is Wo, . . . . . . the work required to get another object with mass 2 mo also initially at rest to a speed vo would be Wo x ___________. The correct answer: 2 See Section 6-3
16.	A ball with a mass of 1.0 kg sits at the top of a 30^o incline plane that is 20.0 meters long. If the potential energy of the ball is 98 J at the top of the incline, what is its potential energy once it rolls half way down the incline? The correct answer: 49 J
17.	How much work must be done to raise a 5.0-kg block of steel from the ground to a height of 2.0 m? The correct answer: 98 N See Sections 6-1, 6-4
18.	A 100-kilogram box is pulled 10 meters across a frictionless horizontal surface by a 50-N force. What is the change in the potential energy of the box?
19.	The work done in raising a body must The correct answer: increase the gravitational potential energy of the body. See Section 6-4
20.	A frictionless incline has a ramp length of 5.0 meters and rises to a height of 4.0 meters. How much work must be done to move a 50 N box from bottom to the top of the incline? The correct answer: 200 J See Sections 6-1, 6-4
21.	A body located 10.0 meters above the surface of the earth has a gravitational potential energy of 490 J relative to the ground. What is the gravitational potential energy, relative to the ground, if the body drops to a height of 7.00 meters above the earth? The correct answer: 343 J See Section 6-4
22.	Three springs of the same relaxed length Lo have spring constants k1 > k2 > k3. The springs are suspended from the ceiling and identical masses are then hung on each of the springs. In response to these identical stretching forces, the springs stretch amounts x1, x2 and x3, respectively. The elongations of the springs are such that __________. The correct answer: x1 < x2 < x3
23.	Three springs of the same relaxed length Lo have spring constants k1 > k2 > k3. The springs are suspended from the ceiling and identical masses are then hung on each of the springs. In response to these identical stretching forces, the springs stretch amounts x1, x2 and x3, respectively. The elastic potential energies stored in each of the three springs are such that __________. The correct answer: EPE1 < EPE2 < EPE3 See Section 6-4
24.	The work required to stretch a relaxed spring with spring constant ko an amount xo is Wo. The additional work required to stretch the spring from xo to 2 xo would be Wo x ____________. The correct answer: 3 See Section 6-4
25.	The work required to stretch a relaxed spring with spring constant ko an amount xo is Wo. The work required to stretch the relaxed spring an amount 3 xo would be Wo x ____________. The correct answer: 9 See Section 6-4
26.	The total energy of a body free falling in a vacuum The correct answer: remains the same.
27.	A block with mass mo on a horizontal, frictionless surface is tied to one end of a massless spring with spring constant ko the other end of which is tied to a vertical wall. The block is pulled aside until the spring has been stretched an amount xo, held at rest and released. When the block passes through its equilibrium position, its speed is vo and its kinetic energy is KEo. If the initial stretch of the spring had been 2 xo, the speed of the block as it passes through its equilibrium position would be vo x ___________. The correct answer: 2 See Section 6-7
28.	A block with mass mo on a horizontal, frictionless surface is tied to one end of a massless spring with spring constant ko the other end of which is tied to a vertical wall. The block is pulled aside until the spring has been stretched an amount xo, held at rest and released. When the block passes through its equilibrium position, its speed is vo and its kinetic energy is KEo. If the spring had been stiffer, i.e., k > ko, the speed of the block as it passed through its equilibrium position would have been _________ vo. The correct answer: more than See Section 6-7
29.	A block with mass mo on a horizontal, frictionless surface is tied to one end of a massless spring with spring constant ko the other end of which is tied to a vertical wall. The block is pulled aside until the spring has been stretched an amount xo, held at rest and released. When the block passes through its equilibrium position, its speed is vo and its kinetic energy is KEo. If the mass of the block had been 4 mo, the speed of the block as it passed through its equilibrium position would have been vo x ____________. The correct answer: 1/2 See Section 6-7
30.	A block with mass mo on a horizontal, frictionless surface is tied to one end of a massless spring with spring constant ko the other end of which is tied to a vertical wall. The block is pulled aside until the spring has been stretched an amount xo, held at rest and released. When the block passes through its equilibrium position, its speed is vo and its kinetic energy is KEo. If the initial stretch of the spring had been 2 xo, the kinetic energy of the block as it passed through its equilibrium position would have been KE = KEo x ____________. The correct answer: 4 See Section 6-7
31.	The rate at which work is being done is The correct answer: power.
32.	What is the power output by a weight lifter lifting a 10^3 N weight a vertical distance of 0.5 meters in 0.1 s?
33.	What is the average power output of a 50-kg boy who climbs a 2.0-m step ladder in 10 seconds? The correct answer: 98 W See Sections 6-4, 6-10
34.	What is the magnitude of the force exerted by air on a plane if 500 kilowatts of power are needed to maintain a constant speed of 100 meters per second? The correct answer: 5000 N
35.	What is the velocity of a car if its engine is doing work at 100 kW and provides a constant force of 5.0 x 10^3 N? The correct answer: 20 m/s See Section 6-10
36.	Two carts A and B have equal masses. Cart A travels up a frictionless incline with a uniform velocity that is twice that of Cart B. Which statement is most accurate? The correct answer: The power developed by A is twice that of B.