Fall 2015 Physics 100 Midterm Exam
(26 questions)

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Unless otherwise stated, ignore air resistance and assume the acceleration of gravity is g = 9.81 m/s2 vertically downward.

QUESTION 1*

A car's initial velocity is along the -x direction. As it slows to a stop, its acceleration points in the -x direction.

(T)   True
(F)   False

QUESTION 2***

A block of mass m is connected by a string over an ideal pulley to another block of mass m as shown. The two blocks have acceleration a. Which of the following statements describes the tension T in the string? (g = +9.81 m/s2)

(a)   T > mg
(b)   T = mg
(c)   T < mg

QUESTION 3***

Two drag cars race. They line up at the starting line at rest. The winning car accelerates at a constant rate a and reaches the finish line with a final velocity v. The losing car accelerates at a constant rate a/4. How far had the losing car traveled, d, when the winning car crossed the finish line?

(a)   d = 2v2/a
(b)   d = v2/a
(c)   d = v2/(2a)
(d)   d = v2/(4a)
(e)   d = v2/(8a)

QUESTION 4**

The next two questions pertain to the following situation:

An inclined plane makes an angle θ with respect to horizontal. A box of mass m sits at rest on the ramp, held in place by friction. The coefficient of static friction is μ.

What is the magnitude of f, the frictional force exerted by the ramp on the box?

(a)   f = mgcosθ
(b)   f = mgsinθ
(c)   f = μmgcosθ

QUESTION 5*

If the angle θ were decreased, how would f change?

(a)   f could increase or decrease depending on the values of m and μ.
(b)   f would increase
(c)   f would decrease

QUESTION 6*

Two rocks are thrown from the top of a cliff at the same time as shown below. One rock is thrown horizontally with velocity v1, while the other rock is thrown at an angle of 60° with respect to the horizontal with velocity v2 = 2v1.

Compare T1, the time it takes for rock 1 to hit the ground, to T2, the time it takes for rock 2 to hit the ground.

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

QUESTION 7*

In the figure below, a block of mass, M1, is being pulled across a frictionless table. A second block of mass, M2, rests on top of block M1. Both blocks are accelerating to the left with a magnitude of a.

Identify all the forces acting on M2 that have components along the x-axis.

(a)   Static friction.
(b)   Static friction and M2a
(c)   Static friction and FPull

QUESTION 8**

Due to prevailing winds, air travel from east to west in the USA takes longer than the same trip from west to east. Suppose that it takes 3 hours to fly the 2000 km from St. Louis to Denver and 2 hours to return. What is the velocity of the wind? Choose the positive direction to be eastward.

(a)   -800.0 km/hr
(b)   -333.3 km/hr
(c)   +166.7 km/hr
(d)   +500.0 km/hr
(e)   +666.7 km/hr

QUESTION 9*

The next two questions pertain to the following situation: The velocity of an object that moves along the x-axis is shown in the plot below. At time t = 0, the object's position was x = 0.

Which of the following statements about x1, the position of the object at time t = t1, is true?

(a)   x1 > 0
(b)   x1 = 0
(c)   x1 < 0

QUESTION 10**

Which of the following statements concerning the determination of the value of t1 is true?

(a)   The time t1 can be correctly calculated knowing only the acceleration and the position at time t = 0
(b)   The time t1 can be correctly calculated knowing only the position and the velocity at time t = 0
(c)   The time t1 can be correctly calculated knowing only the acceleration and the velocity at time t = 0

QUESTION 11*

A block of mass M is pulled upward by a string with tension T = 40 N. The block accelerates upward at a rate a = 5 m/s2. What is the mass of the block?

(a)   M = 8.32 kg
(b)   M = 8.00 kg
(c)   M = 4.08 kg
(d)   M = 2.70 kg
(e)   M = 2.26 kg

QUESTION 12**

The next two questions pertain to the following situation:

A block of mass M1 sits atop a frictionless inclined plane (θ = 20°) and is connected by a massless string over an ideal pulley to another block of mass M2 as shown in the diagram below.

If M1 = 5 kg and M2 = 3kg, in which direction does M2 accelerate?

(a)   M2 accelerates upwards
(b)   M2 does not accelerate
(c)   M2 accelerates downwards

QUESTION 13*

What value of M2 would cause M1 to remain at rest? (M1 is held constant at 5kg)

(a)   M2 = 5.0 kg
(b)   M2 = 1.7 kg
(c)   M2 = 4.7 kg

QUESTION 14*

The next two questions pertain to the following situation:

A quarterback throws a football toward a receiver who catches it t seconds later D meters away. Assume the ball is thrown and caught at the same height above the horizontal field and that you can ignore air resistance.

If t = 3 seconds and D = 60 m, what is the horizontal component v0x of the initial velocity of the ball?

(a)   v0x = 10 m/s
(b)   v0x = 16 m/s
(c)   v0x = 20 m/s
(d)   v0x = 25 m/s
(e)   v0x = 29 m/s

QUESTION 15**

If t = 3 seconds and D = 60 m, what is the maximum height H reached by the ball (above its initial position)?

(a)   H = 5.0 m
(b)   H = 7.7 m
(c)   H = 11 m
(d)   H = 19 m
(e)   H = 44 m

QUESTION 16**

The next two questions pertain to the following situation:

A sign of mass M = 8 kg is suspended from the ceiling. The string on the right is connected to the sign such that it makes an angle of 45° with respect to the horizontal. The string on the left is connected to the sign such that it makes an angle 30° with respect to the horizontal.

How does TL, the tension in the left string, compare to TR, the tension in the right string?

(a)   TL > TR
(b)   TL = TR
(c)   TL < TR

QUESTION 17***

What is TL, the tension in the left string?

(a)   TL = 78.5 N
(b)   TL = 57.5 N
(c)   TL = 43.1 N
(d)   TL= 39.2 N
(e)   TL = 35.9 N

QUESTION 18**

A block of mass m = 3 kg rests on another block of mass M = 5 kg as shown below. A constant force F = 14 N is applied to the bottom block and both blocks are observed to move together with constant acceleration along a frictionless floor. The coefficient of static friction between the two blocks is μs = 0.45

What is the magnitude of the force fmonM, the frictional force the top block (m) exerts on the bottom block (M)?

(a)   fmonM = 22.1 N
(b)   fmonM = 13.2 N
(c)   fmonM = 8.83 N
(d)   fmonM = 5.25 N
(e)   fmonM = 0 N

QUESTION 19**

The next two questions pertain to the following situation:

Three blocks of mass 2 kg, 3 kg, and 4 kg are arranged from left to right in order of increasing mass. The 2 kg block is then pushed with a force F = 60 N across a frictionless floor.

How does F2 on 3, the magnitude of the force the 2 kg block exerts on the 3 kg block, compare to F3 on 4, the magnitude of the force the 3 kg block exerts on the 4 kg block?

(a)   F2 on 3 is smaller than F3 on 4
(b)   They have the same magnitude
(c)   F2 on 3 is larger than F3 on 4

QUESTION 20**

What is the force that the 3 kg block exerts on the 2 kg block?

(a)   5.56 N
(b)   6.67 N
(c)   13.3 N
(d)   38.9 N
(e)   46.7 N

QUESTION 21**

A boy throws a can straight up into the air at speed vcan. If the boy runs at constant speed vboy along the ground, how far away from the ball will he be when it lands?

(a)   2vcan/g
(b)   2vcanvboy/g
(c)   (vcan + vboy)/(2g)

QUESTION 22*

A child runs at speed vc, while an adult runs at speed va. If the adult gives the child a head start of distance d, how long will it take for the adult to catch the child?

(a)   d/(va + vc)
(b)   d/(va - vc)
(c)   (vc + d) / va
(d)   d/va
(e)   d/vc

QUESTION 23**

Gimli and Aragorn are practicing some jumping maneuvers. Gimli stands at the back of a boat of length L. Aragorn is standing on the shore. Gimli runs at constant speed and takes t seconds to reach the end of the boat. While he's running, the boat also moves at constant speed, shifting a distance D to the left.

What is Gimli’s speed with respect to Aragorn while he’s running?

(a)   L/t
(b)   D/t
(c)   (L + D)/t
(d)   (L + D)/(2t)
(e)   (L - D)/t

QUESTION 24***

A boat is traveling at 20 m/s North on a still lake. The boat carries a harpoon gun that fires harpoons at 30 m/s. If the captain fires a harpoon with the gun pointed 40 degrees East of North, how fast will the harpoon be travelling with respect to the water?

(a)   19.3 m/s
(b)   43.6 m/s
(c)   47.1 m/s
(d)   53.5 m/s
(e)   50.0 m/s

QUESTION 25*

In the figure below, a person is swinging a small ball of mass, m, above his head in a circular motion at a constant speed v. The ball is attached to a light string and the radius of the circular path is r

Identify all the forces acting on the ball.

(a)   Tension and weight
(b)   Tension, weight, and mv2/r
(c)   Normal, weight, and mv2/r

QUESTION 26**

A race track is built in a perfect circle so that the length of a lap is 1.5 km, and the road is perfectly flat. If a car is racing at a constant 70mph (31.3m/s), what does the minimum coefficient of friction between the tires and the road have to be to keep the car on the track?

(a)   μmin = 0.27
(b)   μmin = 0.42
(c)   μmin = 0.63