### Fall 2005 Physics 101 Hour Exam 2(26 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 108. The exam period was 90 minutes. The mean score was 88.9; the median was 93. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1*

This and the next three questions concern the same situation:

A rope is attached to a block and a force T = 46 N is applied to pull the block up a rough incline at constant speed.  The incline makes an angle of 30° with the horizontal.  The mass of the block is M = 5 kg, and the block is pulled a distance D = 8 m up the incline.

What is the work done by gravity?

(a)   -196 J
(b)   -100 J
(c)   0 J
(d)   100 J
(e)   196 J

### QUESTION 2*

What is the work done by the tension?

(a)   368 J
(b)   221 J
(c)   0 J

### QUESTION 3*

What is the work done by the normal force of the ramp on the block?

(a)   -196 J
(b)   -100 J
(c)   0 J

### QUESTION 4**

What is the work done by friction?

(a)   0 J
(b)   -172 J
(c)   -196 J

### QUESTION 5*

This and the next two questions concern the same situation:

Two boxes are connected by an ideal string on a frictionless surface as shown below. The pulley is a uniform solid cylinder with radius 0.5 meters and moment of inertia I = 1.5 kg-m2. The boxes are released from rest, and after the top block (M1) has moved 3 meters to the right, it is observed to be traveling with a speed 4 m/s.

What is the mass of the pulley?

(a)   M = 1.5 kg
(b)   M = 8 kg
(c)   M = 12 kg

### QUESTION 6**

Calculate the vertical distance h that block 2 has fallen when block 1 has traveled 3 m.

(a)   h = 0.5 m
(b)   h = 0.8 m
(c)   h = 1.3 m
(d)   h = 1.5 m
(e)   h  = 2.8 m

### QUESTION 7**

The solid cylindrical pulley is replaced by a solid spherical pulley of the same mass and radius and the experiment is repeated. What is the speed of the blocks after the top block is moved 3 m to the right?

(a)   less than 4 m/s
(b)   equal 4 m/s
(c)   greater than 4 m/s

### QUESTION 8*

This and the next two questions concern the same situation:

A 2-meter-long uniform plank has mass 15 kg. It is supported by a fulcrum 0.5 meters from the right end, and by a string attached to the ceiling at the left end as shown in the figure below.

What is the tension Tc in the string attached to the ceiling?

(a)   Tc = 36 N
(b)   Tc = 49 N
(c)   Tc = 110 N

### QUESTION 9*

What is the force of the fulcrum on the plank?

(a)   F = 52 N
(b)   F = 98 N
(c)   F = 135 N

### QUESTION 10**

A box is placed 0.25 meters from the right edge of the plank as shown below. What is the maximum mass this block can have without tipping the plank?

(a)   20 kg
(b)   30 kg
(c)   60 kg

### QUESTION 11*

This and the next question concern the same situation:

Three point masses are attached to a rigid mass-less rod as shown below. The left mass is unknown, the middle mass is 5 kg, and the right mass is 3 kg. The center of mass for this system is 0.55 m to the right of the unknown mass.

Calculate the left-most mass M.

(a)   1 kg
(b)   2 kg
(c)   3 kg

### QUESTION 12*

Calculate the moment of inertia for the system when it is rotated about the axis going through the left mass.

(a)   4.25 kg m2
(b)   6.13 kg m2
(c)   7.75 kg m2

### QUESTION 13**

This and the next question concern the same situation:

A 0.4-meter-long (massless) wrench is being used to tighten a nut as shown in the figure. A torque is being applied by attaching a mass M to a string tied to the end of the wrench. The string is 0.3 meters long and makes an angle of 30° with the wrench.

Calculate the torque exerted on the nut by this configuration.

(a)   0.3 Mg
(b)   0.3 Mg sin(30°)
(c)   0.4 Mg sin(30°)
(d)   0.3 Mg cos(30°)
(e)   0.4 Mg cos(30°)

### QUESTION 14*

As the wrench rotates clockwise (and the angle increases to 60°), the torque exerted on the nut by wrench

(a)   increases.
(b)   remains the same.
(c)   decreases.

### QUESTION 15**

A force F is applied to block A of mass M over a distance D on a horizontal frictionless surface.  The same force F is applied to block B of mass 2M over the same distance.  Both blocks are initially at rest.  Which block ends up with the larger kinetic energy?

(a)   block A
(b)   block B
(c)   Both blocks end up with the same kinetic energy.

### QUESTION 16*

An automobile of mass 1200 kg moving at 1.5 m/s collides with a lamp post and comes to rest.  The collision takes 0.1 s.  What is the total impulse delivered to the automobile?

(a)   1100 kg-m/s
(b)   1200 kg-m/s
(c)   1600 kg-m/s
(d)   1800 kg-m/s
(e)   2400 kg-m/s

### QUESTION 17*

This and the next question concern the same situation:

An object of mass M = 5 kg is moving horizontally in a straight line at a speed of 6 m/s. A force of 100 N is applied over a short period of time such that the speed of the object increases to 10 m/s.

The work done by the force is

(a)   5 J
(b)   15 J
(c)   100 J
(d)   120 J
(e)   160 J

### QUESTION 18*

What is the time period of time over which the force was applied?

(a)   0.15 s
(b)   0.20 s
(c)   0.35 s

### QUESTION 19*

This and the next two questions concern the same situation:

A block sits at rest on a horizontal surface.  It suddenly explodes into two pieces.  A piece of mass 4 kg goes to the left and a piece of mass 8 kg goes to the right.  Each block slides along the frictionless surface, then up a frictionless ramp.  The speed of the 4 kg block is 10 m/s immediately after the explosion.

What is the speed of the 8 kg block immediately after the explosion?

(a)   0 m/s
(b)   2 m/s
(c)   5 m/s
(d)   6 m/s
(e)   8 m/s

### QUESTION 20*

What is the maximum height reached by the 4 kg block on the left slope?

(a)   0.9 m
(b)   3.4 m
(c)   4.5 m
(d)   5.1 m
(e)   7.3 m

### QUESTION 21*

Eventually the two blocks slide back and collide and stick together.  In what direction do the two blocks move immediately after the collision?

(a)   They move to the left.
(b)   They move to the right.
(c)   They do not move.

### QUESTION 22*

This and the next two questions concern the same situation:

Two hockey players are gliding across the ice towards the pack. Player A with mass 75 kg is moving at 3 m/s in the +x direction. Player B with mass 50kg is moving at 4 m/s in the +y direction.

What is the magnitude of their total momentum?

(a)   115 kg m/s
(b)   200 kg m/s
(c)   300 kg m/s
(d)   400 kg m/s
(e)   460 kg m/s

### QUESTION 23*

What direction does their total momentum vector point with respect to the x axis?

(a)   27°
(b)   42°
(c)   62°

### QUESTION 24**

This and the next question concern the same situation:

Player A and Player B are not looking where they are going, and they both collide with Player C, also known as “Tony Zamboni”, at the same instant.  Tony is not moving before the collision and has a mass of 100 kg.  They all collapse together in a heap and drift across the perfectly smooth and frictionless ice.

At what speed are they moving?

(a)   0.85 m/s
(b)   1.33 m/s
(c)   1.65 m/s
(d)   2.00 m/s
(e)   2.45 m/s

### QUESTION 25*

This and the next two questions concern the same situation:

A ship of mass 1.5 × 105 kg and speed 8 m/s strikes a stationary iceberg of mass 1.5 × 106 kg. Assume that the forces exerted by the water on the ship and on the iceberg are negligible.

What is the resulting speed of the iceberg if the ship and the iceberg are stuck together after the collision?

(a)   0.24 m/s
(b)   0.31 m/s
(c)   0.56 m/s
(d)   0.73 m/s
(e)   0.89 m/s

### QUESTION 26***

Let V be the answer to the previous problem.  Suppose that instead of sticking to the iceberg, the ship bounces off the iceberg with speed 4 m/s.  What is now the resulting speed of the iceberg?

(a)   larger than V
(b)   equal to V
(c)   smaller than V

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.