# ASSIGNMENT 5 keys

```ASSIGNMENT 5 keys
1. Knight 5.007. [454965] Show Details
Figure Ex5.7 shows the velocity graph of a 5.0 kg object as it moves along the xaxis. What is the net force acting on this object at the given times?
Figure Ex5.7
t=3s
[20] N
t=5s
[0] N
t=7s
[-30] N
2. Knight 5.009. [370365] Show Details
A horizontal rope is tied to a 46 kg box on frictionless ice. What is the tension in
the rope under each of the following conditions?
(a) the box is at rest
[0] N
(b) the box moves at a steady 5.0 m/s
[0] N
(c) the box has vx = 5.0 m/s and ax = 5.0 m/s2
[230] N
3. Knight 5.006. [484209] Show Details
In each of the two free-body diagrams, the forces are acting on a 2.2 kg object.
For each diagram, find the values of ax and ay, the x- and y-components of the
acceleration, with F1 = 5 N and F2 = 4 N.
(a) Diagram A
ax =
[1.35] m/s2
ay =
[0] m/s2
(b) Diagram B
ax =
[-0.705] m/s2
ay =
[0] m/s2
4. Knight 5.001. [484202] Show Details
The three ropes in the figure are tied to a small, very light ring. Two of the ropes
are anchored to walls at right angles, and the third rope pulls as shown, with T3 =
98 N and = 32°. What are T1 and T2, the magnitudes of the tension forces in the
first two ropes?
T1 =
[83.1] N
T2 =
[51.9] N
5. Knight 5.002. [454971] Show Details
The three ropes in the figure are tied to a small, very light ring. Two of these
ropes are anchored to walls at right angles with tensions T1 = 60 N and T2 = 95
N. What are the magnitude and direction of the tension 3 in the third rope?
Figure Ex5.2
[112] N
[57.7]° (below the positive x-axis)
6. Knight 5.005. [370368] Show Details
In each of the two free-body diagrams, the forces are acting on a 2.4 kg object.
For each diagram, find the values of ax and ay, the x and y components of the
acceleration.
Figure Ex5.5
ax
ay
(a)
[0.833] m/s2
[0] m/s2
(b)
[0.833] m/s2
[0] m/s2
7. Knight 5.010. [370361] Show Details
A 31 kg box hangs from a rope. What is the tension in the rope if the following
are true?
(a) The box is at rest?
[304] N
(b) The box moves up a steady 5.0 m/s?
[304] N
(c) The box has vy = 5.0 m/s and is speeding up at 5.0 m/s2?
[459] N
(d) The box has vy = 5.0 m/s and is slowing down at 5.0 m/s2?
[149] N
8. Knight 5.013. [370363] Show Details
It takes the elevator in a skyscraper 4.0 s to reach its cruising speed of 10 m/s. A
75 kg passenger gets aboard on the ground floor. What is the passenger's
apparent weight at each of the following times?
(a) before the elevator starts moving
[735] N
(b) while the elevator is speeding up
[922] N
(c) after the elevator reaches its cruising speed
[735] N
9. Knight 5.025. [484206] Show Details
A 5.8 kg object initially at rest at the origin is subjected to the time-varying force
shown in Figure P5.25, with the vertical axis in 5 N increments. What is the
object's velocity at t = 6 s?
[3.45] m/s
10. Knight 5.027. [370364] Show Details
A 1300 kg steel beam is supported by two ropes. Each rope has a maximum
sustained tension of 6200 N.
Figure P5.27
Does either rope break? If so, which one(s)?
[x] rope 1
[_] rope 2
[_] none
What is the tension in each rope?
rope 1
[8320] N
rope 2
[5690] N
11. Knight 5.028. [484196] Show Details
A 465 kg piano is being lowered into position by a crane while two people steady
it with ropes pulling to the sides. Bob's rope pulls to the left, 15° below horizontal,
with 500 N of tension. Ellen's rope pulls toward the right, 25° below horizontal.
(a) What tension must Ellen maintain in her rope to keep the piano descending at
[533] N
(b) What is the tension in the main cable supporting the piano?
[4910] N
12. Knight 5.051. [484201] Show Details
A m = 2.3 kg wood box slides down a vertical wood wall while you push on it at a
= 50° angle. What magnitude of force should you apply to cause the box to
slide down at a constant speed?
[25.2] N
13. Knight 5.049. [454983] Show Details
A pickup truck with a steel bed is carrying a steel file cabinet. If the truck's speed
is 20 m/s, what is the shortest distance in which it can stop without the file
cabinet sliding? (Use µs = 0.8 for the coefficient of static friction of steel on steel.)
[25.5] m
14. Knight 5.045. [454936] Show Details
A 2.4 kg wood block is launched up a wooden ramp that is inclined at a 22°
angle. The block's initial speed is 11 m/s. (Use µk = 0.20 for the coefficient of
kinetic friction for wood on wood.)
(a) What vertical height does the block reach above its starting point?
[4.13] m
(b) What speed does it have when it slides back down to its starting point?
[6.39] m/s down the ramp
15. Knight 5.031. [454958] Show Details
Zach, whose mass is 79 kg, is in an elevator descending at 11 m/s. The elevator
takes 3.4 s to brake to a stop at the first floor.
(a) What is Zach's apparent weight before the elevator starts braking?
[774] N
(b) What is Zach's apparent weight while the elevator is braking?
[1030] N
16. Knight 5.039. [484198] Show Details
A 2.9 kg steel block is at rest on a steel table. A horizontal string pulls on the
block.
(a) What is the minimum string tension needed to move the block?
[22.7] N
(b) If the string tension is 29 N, what is the block's speed after moving 1.0 m?
[2.87] m/s
(c) If the string tension is 29 N and the table is coated with oil, what is the block's
speed after moving 1.0 m?
[4.36] m/s
```
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