### Fall 1999 Physics 101 Hour Exam 2(29 questions)

The grading button and a description of the scoring criteria are at the bottom of this page.

This exam consists of 29 questions; 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 126. When the exam was given, the minimum "A" score was 112; the minimum "B" was 97; the minimum "C" was 82; the minimum "D" was 63. The mean was 99.4; the median was 102. Click here to see the formula sheet that came with the exam.

### QUESTION 1***

This and the next four questions are about the following situation:

Two blocks slide towards each other on a frictionless surface. Block 1 has mass 6 kg and slides to the right with speed 15 m/s. Block 2 of unknown mass slides to the left with speed 15 m/s. The blocks collide, stick together and move to the right with velocity vf = 5 m/s.

Compare the magnitude of the net impulse on block 1, I1, with the magnitude of the net impulse on block 2, I2, during the collision.

(a)   I1 > I2
(b)   I1 = I2
(c)   I1 < I2

### QUESTION 2*

What is M2, the mass of block 2?

(a)   M2 = 0.67 kg
(b)   M2 = 3.0 kg
(c)   M2 = 6.0 kg
(d)   M2 = 18 kg
(e)   M2 = 54 kg

### QUESTION 3*

What is the KE1f, kinetic energy of block 1 after the collision?

(a)   KE1f = 0 J
(b)   KE1f = 30 J
(c)   KE1f = 50 J
(d)   KE1f = 75 J
(e)   KE1f = 100 J

### QUESTION 4**

What is the net impulse I2 on block 2 during the collision?

(a)   I2 = 12 Ns
(b)   I2 = 30 Ns
(c)   I2 = 24 Ns
(d)   I2 = 60 Ns
(e)   I2 = 72 Ns

### QUESTION 5*

Which of the following statements best describes what happens to the two-block system during the collision?

(a)   Total momentum and kinetic energy are both conserved.
(b)   Kinetic energy is conserved but total momentum is not.
(c)   Total momentum is conserved but kinetic energy is not.

### QUESTION 6*

A block is moved 2.5 meters across a floor by two 20 N forces. The force F1 pushes at an angle down, and the force F2 pushes directly horizontally. Compare W the work done by the two forces.

(a)   W1 < W2
(b)   W1 = W2
(c)   W1 > W2

### QUESTION 7*

This and the next three questions are about the following situation:

A block sits at rest on a horizontal surface. It suddenly explodes into two pieces. A piece of mass 5 kg goes to the left and a piece of mass 20 kg goes to the right. The blocks each slide along the surface, then up a ramp. The speed of the 5 kg block is 8 m/s immediately after the explosion.

Compare the magnitude of the velocities of the two pieces just after the explosion.

(a)   |v5| < |v20|
(b)   |v5| = |v20|
(c)   |v5| > |v20|

### QUESTION 8*

Compare the magnitude of the momentum of the two pieces just after the explosion.

(a)   |p5| < |p20|
(b)   |p5| = |p20|
(c)   |p5| > |p20|

### QUESTION 9*

What is the speed v20 of the 20 kg block just after the explosion?

(a)   v20 = 0.50 m/s
(b)   v20 = 2.00 m/s
(c)   v20 = 3.00 m/s
(d)   v20 = 4.00 m/s
(e)   v20 = 8.00 m/s

### QUESTION 10*

What is the maximum height h reached by the 5 kg block?

(a)   h = 5.20 m
(b)   h = 3.26 m
(c)   h = 1.20 m
(d)   h = 0.82 m
(e)   h = 0.38 m

### QUESTION 11***

This and the next three questions are about the following situation:

A car is moving with speed Vcar = 30 m/s down a straight road. The tires roll without slipping on the ground, and are spinning with angular velocity w = 100 rad/s.

With respect to the ground, what is the speed Vtop of a point on the very top of the tire (see picture)?

(a)   Vtop = 0
(b)   Vtop = Vcar
(c)   Vtop = 2 Vcar

### QUESTION 12*

Calculate R the radius of the wheel.

(a)   R = 0.13 m
(b)   R = 0.24 m
(c)   R = 0.30 m
(d)   R = 0.41 m
(e)   R = 0.52 m

### QUESTION 13**

The car puts on the brakes and comes to rest in a time Dt. If the radius of the tires is R, what is the magnitude of the average angular acceleration of the wheels while the car is slowing down?

(a)   |aave| = Vcar / (R Dt)
(b)   |aave| = R Vcar / Dt
(c)   |aave| = Vcar Dt / R

### QUESTION 14*

Suppose the magnitude of the angular acceleration of the wheel while braking is a = 15 rad/s2. How many revolutions n does the wheel make after the brakes are applied before coming to a stop?

(a)   n = 8.2 revolutions
(b)   n = 14 revolutions
(c)   n = 27 revolutions
(d)   n = 43 revolutions
(e)   n = 53 revolutions

### QUESTION 15*

This and the next two questions are about the following situation:

A piece of modern art is made by hanging a box of doughnuts from one end of a 2m long uniform wooden rod. The rod itself hangs by a wire attached to the ceiling (see the picture below). The mass of the box of doughnuts is 1 kg, the mass if the rod is 2 kg, and the whole object is in static equilibrium.

What is the tension T in the wire supporting the rod?

(a)   T = 9.8 N
(b)   T = 19.6 N
(c)   T = 29.4 N
(d)   T = 35.7 N
(e)   T = 58.8 N

### QUESTION 16**

What distance d from the left end of the rod is the wire attached?

(a)   d = 0.75 m
(b)   d = 0.67 m
(c)   d = 0.49 m
(d)   d = 0.33 m
(e)   d = 0.25 m

### QUESTION 17**

If this piece of modern art were to be balanced on the moon (g < 9.8 m/s2), the distance d of the string from the left end of the rod would

(a)   increase.
(b)   decrease.
(c)   remain the same.

### QUESTION 18*

This and the next question are about the following situation:

One end of a board is attached to a wall by a hinge, and the other end is kept from rotating downward by a wire, also attached to the wall (see picture). In case 1 the wire is attached to the end of the board, and in case 2 it is attached to the center of the board. In both cases the horizontal board has the same (non-zero) mass and length, and the wire makes the same angle with the board.

Compare the tension T of the wires in the two systems.

(a)   T1 < T2
(b)   T1 = T2
(c)   T1 > T2

### QUESTION 19**

Compare the torque t about the hinge due to the wire in the two systems.

(a)   t1 < t2
(b)   t1 = t2
(c)   t1 > t2

### QUESTION 20**

This picture shows two different ways of using a wrench to loosen a stuck nut. The magnitude of the applied force F is the same in each case. The torque produced on the nut in the two cases is t1 and t2 respectively. Which of the following statements about the magnitudes of these torques is correct?

(a)   t1 < t2
(b)   t1 = t2
(c)   t1 > t2

### QUESTION 21*

This and the next four questions are about the following situation:

A skier with a mass of 50 kg starts from the top of a hill at height h above ground. The skier glides down the hill to point A where her velocity is vA = 20 m/s and continues up a second hill 8 meters high and back down the other side. Her entire trip up to point C is frictionless. At point C she begins stopping and comes to a complete stop 48 meters later at point D.

What is the height h of the hill?

(a)   h = 11.1 m
(b)   h = 16.2 m
(c)   h = 20.4 m
(d)   h = 28.5 m
(e)   h = 33.1 m

### QUESTION 22**

What is the speed vB of the skier when she reaches point B?

(a)   vB = 9.64 m/s
(b)   vB = 11.2 m/s
(c)   vB = 12.5 m/s
(d)   vB = 15.6 m/s
(e)   vB = 23.6 m/s

### QUESTION 23**

What is the magnitude of the average stopping force FCD from C to D?

(a)   FCD = 81.6 N
(b)   FCD = 208 N
(c)   FCD = 282 N
(d)   FCD = 328 N
(e)   FCD = 490 N

### QUESTION 24*

A second heavier skier with mass 75 kg skis down the same hill. What is the magnitude of his velocity v at point A?

(a)   v < 20 m/s
(b)   v = 20 m/s
(c)   v > 20 m/s

### QUESTION 25**

At point C, he applies the same average stopping force as the lighter skier did, what distance s will he travel before stopping?

(a)   s < 48 m
(b)   s = 48 m
(c)   s > 48 m

### QUESTION 26*

This and the next question are about the following situation:

You are on the crew of the space shuttle performing extra-vehicular activity. You are slowly drifting away from the shuttle at a constant speed of 5 m/s. You decide that you are getting dangerously far from the shuttle and want to reverse your direction. You decide to throw the 10 kg tool kit you are carrying.

In what direction should you throw the tool kit in order to achieve your desire to move toward the shuttle.

(a)   Toward the shuttle
(b)   Away from the shuttle
(c)   It makes no difference

### QUESTION 27***

Your mass is 100 kg and the mass of the tool kit is 10 kg. How fast should you throw the tool kit (with respect to the shuttle) in order that your final velocity is 2 m/s toward the shuttle.

(a)   20 m/s
(b)   35 m/s
(c)   50 m/s
(d)   64 m/s
(e)   75 m/s

### QUESTION 28*

This and the next question are about the following situation:

Two identical blocks are a distance h = 0.4 meters above the ground. Block 1 is dropped straight down, block 2 slides down a frictionless ramp of length L = 1 meter.

Compare the velocity of block 1 just before it reaches the ground v1, with the velocity of block 2 just before it reaches the ground v2.

(a)   v1 > v2
(b)   v1 = v2
(c)   v1 < v2

### QUESTION 29*

Compare the amount of time t it takes each block to reach the ground.

(a)   t1 > t2
(b)   t1 = t2
(c)   t1 < t2

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.