### Spring 2007 Physics 101 Hour Exam 3(25 questions)

The grading button and a description of the scoring criteria are at the bottom of this page. Basic questions are marked by a single star *. More difficult questions are marked by two stars **. The most challenging questions are marked by three stars ***.

True-false questions are worth 2 points each, three-choice multiple choice questions are worth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 110. The exam period was 90 minutes; the average score was 88.5; the median score was 92. Click here to see page1 page2 of the formula sheet that came with the exam.

Unless told otherwise, you should assume that the acceleration of gravity near the surface of the earth is 9.8 m/s2 downward and ignore any effects due to air resistance.

### QUESTION 1*

This and the following question relate to the same situation:

A hydraulic lift with a rectangular platform of area A = 9 m2 is used to raise cars above the ground. The cross-sectional area of the narrow, fluid-filled tube connected to the lift-platform is 0.05 m2 (as shown in the figure).

If a 720-kg car is placed on the lift-platform what force F must be applied to the small piston to balance the weight of the car?

(a)   9.8 N
(b)   14.3 N
(c)   28.4 N
(d)   39.2 N
(e)   46.5 N

### QUESTION 2*

Through what distance must the piston in the small tube be forced downwards to raise the car up 2.2 cm?

(a)   d = 23 cm
(b)   d = 147 cm
(c)   d = 396 cm

### QUESTION 3*

This and the following two questions relate to the same situation:

Water (ρw = 1000 kg/m3) flows though a cylindrical pipe of radius R1 = 8 cm with an unknown speed of v1. The pipe then narrows to a radius R2 = 3.2 cm where the water has a speed of v2 = 8.13 m/s.

What is the speed of the water in the wide region of the pipe?

(a)   v1 = 1.3 m/s
(b)   v1 = 3.3 m/s
(c)   v1 = 8.1 m/s
(d)   v1 = 20 m/s
(e)   v1 = 51 m/s

### QUESTION 4**

How long would it take for this pipe to fill a swimming pool with a volume of 50 m3 ?

(a)   1.9 × 103 s
(b)   3.9 × 103 s
(c)   4.3 × 103 s
(d)   5.1 × 103 s
(e)   6.8 × 103 s

### QUESTION 5*

What is the difference in pressure, P1 - P2 ?

(a)   4 kPa
(b)   18 kPa
(c)   32 kPa
(d)   41 kPa
(e)   55 kPa

### QUESTION 6*

This and the following question relate to the same situation:

A string is attached to a cube of wood of volume V = 0.3 m3 that is placed in fresh water with density 1000 kg/m3, as shown in the figure below. The tension in the string, T, is 520 N.

What is the density of the wood?

(a)   212 kg/m3
(b)   496 kg/m3
(c)   614 kg/m3
(d)   823 kg/m3
(e)   1043 kg/m3

### QUESTION 7*

If the fresh water were replaced by seawater of density 1030 kg/m3, the tension in the string would be

(a)   smaller than 520 N
(b)   equal to 520 N
(c)   larger than 520 N

### QUESTION 8*

An open U shaped tube is initially partially filled with water (ρw = 1000 kg/m3). An 10 cm high column of oil (ρoil = 800 kg/m3) is carefully poured into the right side of the tube (see picture). What is the height H of the oil above the water?

(a)   H = 1 cm
(b)   H = 2 cm
(c)   H = 3 cm
(d)   H = 4 cm
(e)   H = 5 cm

### QUESTION 9*

This and the following question relate to the same situation:

A block suspended from a scale has a weight of 3 N. The block is then lowered into a glass of water so that it is completely submerged and the reading on the scale is 2.4 Newtons. (The density of water is 1000 kg/m3).

What is the volume of the block?

(a)   8.94 × 10-6 m3
(b)   3.01 × 10-5m3
(c)   6.12 × 10-5 m3
(d)   1.04 × 10-5 m3
(e)   4.06 × 10-4 m3

### QUESTION 10*

If the block was lowered deeper in the water, but not touching the bottom of the glass, the reading on the scale would

(a)   remain at 2.4 N.
(b)   increase.
(c)   decrease.

### QUESTION 11*

You are holding a barometer and standing on the ground floor of a tall building. You then go to the top floor and notice that the reading on your barometer has dropped by 5062 Pa. How tall is the building? (Assume the density of air is constant and equals 1.29 kg/m3)

(a)   100 m
(b)   200 m
(c)   300 m
(d)   400 m
(e)   500 m

### QUESTION 12**

A balloon of a fixed volume 1200 m3 has a mass of 400 kg (when empty). When full of helium, what is the maximum mass it can lift off the ground? The density of helium is 0.18 kg/m3 and the density of air is 1.29 kg/m3.

(a)   128 kg
(b)   332 kg
(c)   480 kg
(d)   594 kg
(e)   932 kg

### QUESTION 13*

This and the following three questions relate to the same situation:

A 7.0 kg block is resting on a horizontal frictionless surface. A force F pushes the block to the right and a spring with spring constant 150 N/m pushes the block to the left, such that the block is in equilibrium. At time t = 0 the force F is removed and the mass oscillates back and forth with a maximum speed v = 2.1 m/s.

How long does it take the block to complete one oscillation?

(a)   0.43 s
(b)   1.2 s
(c)   1.4 s

### QUESTION 14*

What is the magnitude of the force F that originally compressed the spring?

(a)   F = 68 N
(b)   F = 73 N
(c)   F = 91 N
(d)   F = 120 N
(e)   F = 150 N

### QUESTION 15**

How fast is the block moving, when the spring is compressed 0.27 m from its equilibrium position?

(a)   1.21 m/s
(b)   1.69 m/s
(c)   1.79 m/s
(d)   2.05 m/s
(e)   2.41 m/s

### QUESTION 16***

Which function best describes the velocity of the block as a function of time?

(a)   v(t) = Vmax cos(ωt)
(b)   v(t) = -Vmax cos(ωt)
(c)   v(t) = -Vmax sin(ωt)

### QUESTION 17*

This and the following question relate to the same situation:

A simple 3 kg pendulum is suspended from the ceiling of an elevator. When the elevator is at rest, the period of the pendulum is 0.75 seconds.

What is the length of the pendulum string?

(a)   0.14 m
(b)   0.24 m
(c)   0.34 m

### QUESTION 18*

While riding in the elevator, you notice the period of the pendulum is 0.6 seconds. What can you conclude about the motion of the elevator? The elevator is

(a)   moving up with a constant speed.
(b)   moving down with a constant speed.
(c)   accelerating up.
(d)   accelerating down.
(e)   at rest and it is not accelerating.

### QUESTION 19**

This and the following two questions relate to the same situation:

Standing 10 meters from a stopped ambulance, you notice the siren is 120 dB and the pitch is 500 Hz. Another day, while standing by the side of a road, you see the same ambulence driving and hear the siren but it is only 80 dB and the pitch is 540 Hz. (The speed of sound in air is 340 m/s.)

What is the speed of the ambulance?

(a)   27 m/s
(b)   25 m/s
(c)   23 m/s

### QUESTION 20**

What direction is the ambulance going?

(a)   toward you
(b)   away from you.

### QUESTION 21**

How far away is the ambulance?

(a)   100 m
(b)   1000 m
(c)   10000 m

### QUESTION 22*

This and the following two questions relate to the same situation:

A harpsichord string (fixed at both ends) is 0.8 meters long. The fundamental frequency is 500 Hz and the tension in the string is 158 newtons. (The speed of sound in air is 340 m/s.)

What is the speed of the transverse wave in the string?

(a)   600 m/s
(b)   700 m/s
(c)   800 m/s

### QUESTION 23*

What is the linear mass density of the string?

(a)   2.5 × 10-4 kg/m
(b)   3.5 × 10-4 kg/m
(c)   4.5 × 10-4 kg/m

### QUESTION 24*

What is the wavelength of the sound wave (propagating in air) produced by this string?

(a)   0.68 m
(b)   0.80 m
(c)   1.5 m

### QUESTION 25**

What is the wavelength of the transverse wave of the string corresponding to its second harmonic?

(a)   0.53 m
(b)   0.78 m
(c)   0.91 m

Scoring of True-False (T,F) Questions:
• If you mark the correct answer, you get 2 points.
• If you mark the wrong answer or if you mark neither answer, you get 0 points.
Scoring of Multiple Choice I (a,b,c) Questions:
• If you mark the correct answer, you get 3 points.
• If you mark a wrong answer or if you mark none of the answers, you get 0 points.
Scoring of Multiple Choice II (a,b,c,d,e) Questions:
• If you mark one answer and it is the correct answer, you get 6 points.
• If you mark two answers and one of them is the correct answer, you get 3 points.
• If you mark three answers and one of them is the correct answer, you get 2 points.
• If you do not mark the correct answer, or if you mark more than three answers, or if you mark none of the answers, you get 0 points.