Physics 121 Practice Hour Exam 1
(21 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 ***.

This exam consists of 21 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 84.

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 car is initially moving at a speed of 25 km/hr when the brakes are applied, resulting in a constant deceleration that brings the car to rest in 15 m. Assuming the same constant deceleration, what would the stopping distance be if the initial speed were 50 km/hr ?

(a)   30 m
(b)   45 m
(c)   60 m

QUESTION 3*

This and the following question concern the same physical situation.

You and a friend are standing on a bridge. You decide to drop a rock from a height of 80 m from the water, while your friend decides to throw a rock from the same height with an initial horizontal velocity of 20 m/s.

How long does it take for your rock to hit the water?

(a)   2.14 sec
(b)   4.04 sec
(c)   5.13 sec
(d)   6.81 sec
(e)   7.28 sec

QUESTION 4*

How far from the base of the bridge does your friend’s stone land?

(a)   42.8 m
(b)   56.3 m
(c)   75.6 m
(d)   80.8 m
(e)   145.6 m

QUESTION 5*

A drag car starts from rest and races the 1/4 mile. If it accelerates at a constant rate for the entire race, then it will reach half its maximum speed at the 1/8 mile mark (half the race distance).

(T)   True
(F)   False

QUESTION 6**

Two blocks of masses m and 2m are placed in contact on a horizontal, frictionless surface, with the more massive block on the left. A force of magnitude F, pointing to the right, is applied to the more massive block. What is the net force on the more massive block?

(a)   F
(b)   F/3
(c)   2F/3

QUESTION 7*

A kid ties a rock to the end of a string and spins it in a circular path in the vertical plane. The speed of the rock is constant. When the rock is at the bottom of the circle, which of the following is true about the tension T in the string?

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

QUESTION 8***

An inclined plane makes an angle q 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 the frictional force exerted by the ramp on the box?

(a)   mgsinq
(b)   µmgcosq
(c)   µmg

QUESTION 9***

This and the following question concern the same physical situation.

A block of mass m rests on another block of mass M ( M > m) as shown below. A constant force F is applied to the bottom block (mass M) and both blocks are observed to move together with constant acceleration a along a frictionless floor (i.e. m does not slip relative to M). Let f represent the frictional force the bottom block (M) exerts on the top block (m).

What is the direction of the force f ?

(T)   f points to the left
(F)   f points to the right

QUESTION 10***

What is the magnitude of the force f ?

(a)   f = µSmg
(b)   f = µSMg
(c)   f = µS(M+m)g
(d)   f = ma
(e)   f = Ma

QUESTION 11*

A block of mass 20 kg is free to slide on a horizontal frictionless surface. A force F is applied as shown in the drawing, where the angle that the force makes with the horizontal is 30°. As a result, the block has a horizontal acceleration of 50 m/s2. What is the magnitude of F?

(a)   1000 N
(b)   1155 N
(c)   1267 N
(d)   1350 N
(e)   2875 N

QUESTION 12*

This and the following two questions concern the same physical situation.

Two boats, each capable of moving in still water at a constant velocity v = 6 m/s, set out to cross a river of width W = 20 m. Boat 1 heads directly across the river while boat 2 is pointed at an angle q = 60 degrees with respect to the shore as shown in the diagram below. The current in the river moves at speed v0 = 2 m/s as shown.

Which boat takes the least amount of time to cross the river?

(T)   Boat 1
(F)   Boat 2

QUESTION 13*

Which boat moves with the greater speed with respect to the shore?

(T)   Boat 1
(F)   Boat 2

QUESTION 14**

How far downstream (D) is boat 2 when it reaches the other side of the river?

(a)   19.3 m
(b)   32.6 m
(c)   45.8 m
(d)   57.7 m
(e)   67.1 m

QUESTION 15**

City A and City B are located 10 km apart on the bank of a very straight river. You need to travel from city A to City B and back to City A. There is a road located next to the river and the distance between cities along the road and the river are the same. You have the option of taking a boat down the river and returning up the river in the boat or you can drive a car on the road and return in the car. The car can travel at 30 m/s and the boat can travel at 30 m/s. The river has a velocity of 10 m/s. Compare the time it will take you to make one round trip in the car, Tc to the time it will take you to make one round trip in the boat, Tb.

(a)   Tc > Tb
(b)   Tc = Tb
(c)   Tc < Tb

QUESTION 16**

This and the following two questions concern the same physical situation.

Three blocks are pushed up a frictionless plane that is inclined at an angle of 30 degrees with respect to the horizontal as shown below. The blocks move together with constant acceleration a = 3.0 m/s2. The acceleration is up the incline. The masses of the blocks are: MA = MC = 1 kg, and MB = 2 kg. The next three questions pertain to this situation.

The force that block A exerts on Block B is greater than the force that block B exerts on Block A.

(T)   True
(F)   False

QUESTION 17**

Compare FAonB, the force Block A exerts on Block B, to FConB, the force Block C exerts on Block B:

(a)   FAonB < FConB
(b)   FAonB = FConB
(c)   FAonB > FConB

QUESTION 18**

What is the value of F, the external force that is exerted on Block A?

(a)   20.3 N
(b)   31.6 N
(c)   39.8 N
(d)   43.2 N
(e)   56.9 N

QUESTION 19**

A block of mass M = 10 kg is attached to a massless ring that is suspended by two strings to walls as shown in the figure. Each string makes an angle q = 60° to the horizontal. What is TL, the tension in the left string?

(a)   TL = 40.2 N
(b)   TL = 56.6 N
(c)   TL = 65.1 N
(d)   TL = 80.4 N
(e)   TL = 114 N

QUESTION 20*

This and the following question concern the same physical situation.

A quarterback throws a football toward a receiver who catches it 3.0 seconds later 60 meters away. Assume the ball is thrown and caught at the same height above the horizontal field and ignore air resistance.

What is the horizontal component v0x of the initial velocity of the ball?

(a)   0 m/s
(b)   10 m/s
(c)   15 m/s
(d)   20 m/s
(e)   30 m/s

QUESTION 21*

What is the maximum height H reached by the ball (above its initial position).

(a)   9 m
(b)   10 m
(c)   11 m
(d)   12 m
(e)   13 m