Download Chap7 1. Test Bank, Question 25 2. Test Bank, Question 11 3

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Chap7
1. Test Bank, Question 25
At time t = 0 a 2-kg particle has a velocity in m/s of
At t = 3 s its velocity is
During this time the work done on it was:
4J
–4 J
–12 J
–40 J
2. Test Bank, Question 11
An object moves in a circle at constant speed. The work done by the centripetal force is zero because:
the displacement for each revolution is zero
the average force for each revolution is zero
there is no friction
the magnitude of the acceleration is zero
the centripetal force is perpendicular to the velocity
3. Chapter 7, Concept Question 2
Figure 7-15a shows two horizontal forces that act on a block that is sliding to the right across a frictionless floor. Figure
7-15b shows three plots of the block’s kinetic energy K versus time t. Which of the plots best corresponds to the
following three situations:
(a) F1 = F2, (b) F1 > F2, (c) F1 < F2?
Figure 7-15
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(a) F1 = F2 2
(b) F1 > F2 3
(c) F1 < F2 1
1. plot 1
2. plot 2
3. plot 3
4. Test Bank, Question 24
At time t = 0 a particle starts moving along the x axis. If its kinetic energy increases uniformly with t the net force acting
on it must be:
constant
proportional to t
inversely proportional to t
5. Test Bank, Question 30
A crate is initially at rest on a horizontal frictionless table. A constant horizontal force F is applied. Which of the following
five graphs is a correct plot of work W as a function of crate speed v?
I
II
III
IV
V
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6. Test Bank, Question 4
An object is constrained by a cord to move in a circular path of radius 0.5m on a horizontal frictionless surface. The
cord will break if its tension exceeds 16N. The maximum kinetic energy of the object can have is:
4J
8J
16 J
32 J
64 J
7. Test Bank, Question 16
Camping equipment weighing 6000 N is pulled across a frozen lake by means of a horizontal rope. The coefficient of
kinetic friction is 0.05. How much work is done by the campers in pulling the equipment 1000 m if its speed is
increasing at the constant rate of 0.20 m/s2?
–1.2 × 106 J
1.8 × 105 J
3.0 × 105 J
4.2 × 105 J
1.2 × 106 J
8. *Chapter 7, Problem 43
A force of 5.8 N acts on a 28 kg body initially at rest. Compute the work done by the force in (a) the first, (b) the
second, and (c) the third seconds and (d) the instantaneous power due to the force at the end of the third second.
(a) Number
0.600714285714
Units J
(b) Number
1.802142857143
Units J
(c) Number
3.003571428571
Units J
(d) Number
3.604285714286
Units W
9. *Chapter 7, Problem 15
The figure shows three forces applied to a trunk that moves leftward by 2.89 m over a frictionless floor. The force
magnitudes are F1 = 4.91 N, F2 = 8.92 N, and F3 = 3.06 N, and the indicated angle is θ = 60°. (a) During the
displacement, what is the net work done on the trunk by the three applied forces, the gravitational force, and the
normal force? (b) Is there a net transfer of energy to or from the trunk? (c) Does the kinetic energy of the trunk
increase or decrease?
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(a) Number
(b) to
(c) increase
1.300500000000
Units J
Significant digits are disabled; the tolerance is +/-5%
10. *Chapter 7, Problem 57
A 265 kg crate hangs from the end of a rope of length L = 13.6 m. You push horizontally on the crate with a varying
force
to move it distance d = 3.88 m to the side (Fig. 7-43). (a) What is the magnitude of
when the crate is in this
final position? During the crate's displacement, what are (b) the total work done on it, (c) the work done by the
gravitational force on the crate, and (d) the work done by the pull on the crate from the rope? (e) Knowing that the
crate is motionless before and after its displacement, use the answers to (b), (c), and (d) to find the work your force
does on the crate.
Figure 7-43
Problem 57.
(a) Number
773.036194532125
(b) Number
0
(c) Number
-1467.865346985213
(d) Number
0
(e) Number
1467.865346985213
Units N
Units J
Units J
Units J
Units J
11. Test Bank, Question 49
Three identical springs (X,Y,Z) are arranged as shown. When a 4.0-kg mass is hung on X, the mass descends 3.0 cm.
When a 6.0-kg mass is hung on Y, the mass descends:
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2.0 cm
4.0 cm
4.5 cm
6.0 cm
9.0 cm
12. *Chapter 7, Problem 27
A spring and block are in the arrangement of Fig. 7-11.
Fig. 7-11
When the block is pulled out to x = +4.0 cm, we must apply a force of magnitude 370 N to hold it there. We pull the
block to x = 12.0 cm and then release it. How much work does the spring do on the block when the block moves from
xi=+6.0 cm to (a)x= +4.0 cm, (b)x=-4.0 cm, (c)x=-6.0 cm, and (d)x=-9.0 cm?
(a) Number
9.25
Units J
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(b) Number
9.25
Units J
(c) Number
0
(d) Number
-20.8125
Units J
Units J
13. *Chapter 7, Problem 62
A 210 g block is dropped onto a relaxed vertical spring that has a spring constant of k = 3.9 N/cm (Fig. 7-44). The block
becomes attached to the spring and compresses the spring 11 cm before momentarily stopping. While the spring is being
compressed, what work is done on the block by (a) the gravitational force on it and (b) the spring force? (c) What is
the speed of the block just before it hits the spring? (Assume that friction is negligible.) (d) If the speed at impact is
doubled, what is the maximum compression of the spring?
Fig. 7-44
Problem 62.
(a) Number
0.22638
Units J
(b) Number
-2.3595
Units J
(c) Number
4.507263978450
Units m/s
(d) Number
0.214523556525
Units m
14. *Chapter 7, Problem 61
What work is done by a force
m)
+ (6 m)
Number
-256
to a position
= (7x N)
f
= -(5 m)
+ (6 N) , with x in meters, that moves a particle from a position
i
= (9
- (4 m) ?
Units J
Significant digits are disabled; the tolerance is +/-5%
15. *Chapter 7, Problem 41
A single force acts on a 1.0 kg particle-like object in such a way that the position of the object as a function of time is
given by x = 1.5t - 0.86t2 + 3.8t3, with x in meters and t in seconds. Find the work done on the object by the force from
t = 0 to t = 8.5 s.
Number
328478.31545
Units J
Significant digits are disabled; the tolerance is +/-5%
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16. *Chapter 7, Problem 48
A 0.29 kg ladle sliding on a horizontal frictionless surface is attached to one end of a horizontal spring (k = 220 N/m)
whose other end is fixed. The ladle has a kinetic energy of 16 J as it passes through its equilibrium position (the point at
which the spring force is zero). (a) At what rate is the spring doing work on the ladle as the ladle passes through its
equilibrium position? (b) At what rate is the spring doing work on the ladle when the spring is compressed 0.090 m and
the ladle is moving away from the equilibrium position?
(a) Number
0
Units W
(b) Number
-202.115234457970
Units W
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