Energy & Matter

  Sample Exam I:  NO CELL PHONES OR OTHER COMMUNICATION DEVICES

Multiple Choice:  (2 points each)  Put your answers on the Scantron. Choose the Best Answer(s).

Let me know if you have erasures on your Scantron.

1.      If I drop a feather and a lead weight at the same time in air, e.g. in this room,

A) the feather will reach the ground first.

B) the lead weight will reach the ground first.

C) they will reach the ground at the same time.

2.      If I double the net force on an object, its

A)  acceleration doubles.

B)  mass doubles.

C)  velocity doubles

3.      If a box is moving and the net force on it becomes zero

A)  it will gradually slow to a stop.

B)  it will speed up.

C)  it will continue the accelerate with the acceleration it had when the force became zero.

D)  it will continue to move with the velocity it had when the force became zero.

4.      If a 20 kg wagon is pulled along with a constant acceleration of 5m/s2, the net force on it is

A)  0N                        B)  200N                    C)  4N               D)  0.25N          E) 100N

5.      A 4 kg mass is initially moving with a speed of 10m/s to the right.  Then I apply a force toward the left of 5N as the mass moves 2m to the right.  (Assume this is the net force on it.)  The speed of the mass will

A)  stay the same                         B)  increase                         C)  decrease

6.      When a 1 kg falling object has reached terminal velocity

A)  its speed is 10m/s                            B) its acceleration is 10m/s2

C)  the net force on it is 10N                 D) its acceleration is zero

7.      A car travels around a curve with a constant speed of 10m/s.  During that time the

A)  The net force on the car was zero.

B)  The acceleration of the car was zero

C)  The net force on the car was not zero.

D)  The velocity was constant.

8.      I weigh 700N and jump off a table and fall toward the earth.  As I fall

A)  I experience no net force because I’m in freefall.

B)  My speed is constant

C)  I exert an upward force of 700N on the earth

D)  I exert a downward force of 700N on the earth

9.      Which of the following is a vector or are vectors?

A)  mass            B)  time             C)  momentum            D)  speed

10.    I am running with a speed of 5m/s.  How long will it take for me to go 200m?

A)  0.025s                  B)  40s                       C)  1000s

11.    Which of the following could be a scientific hypothesis?

A)     The moon is made of cheese.

B)     There are parts of the universe we will never discover.

C)     The universe if filled with undetectable particles

12.     A total force of 9N is applied to a Mass and its acceleration is 3 m/s2.  Its mass is

A)  0.33kg          B)  0.9kg            C)  27kg.            D)  3kg

13.    If a 20 kg wagon is pulled along with a constant velocity of 5m/s, the net force on it is

A)  0N                       B)  200N                    C)  100N            D)  0.25N

14.     A car accelerates in a straight line from rest to a speed of 10 m/s in 10 s, moving 40 m in that time.  Its average acceleration was

A)  10 m/s2        B)  5 m/s2          C)  0.4 m/s2                D)  1m/s2           E)  0.25m/s2

15.     An object weights 25 N.  Its mass is

A)  25 kg           B)  25 lb.           C)  2.5 kg           D)  0.25 kg

16.    I am standing on two scales, with one foot on each scale.  My weight is 800N and I am holding a sack of cement.  One scale reads 300N and the other reads 700N.  The bag of cement weighs

        A)  400N            B)  500N            C)  100N            D)  200N

17.    You want to stop a fast-moving object.  You will stop it with a larger force if you decrease its momentum over a

A)  longer time            B)  shorter time           C)  the time is not a factor

18.    If I am moving  with a constant speed in the same direction it means that

A)  there are not any forces acting on me

B)  the net force on me  is zero

C)  the net force on me is constant

19.    I am applying a horizontal force of 40N in an eastward direction to a box weighing 100N as I push it across a level floor with a constant velocity of 2m/s to the eastward.  If friction is the only other horizontal force on the box, the frictional force the floor exerts on the box is

A)  40N westward

B)  100N westward

C)  40N eastward

D)  60N westward

E)  60N eastward

20.    It takes a net force of 600N to hold up a box on the earth with no acceleration.  On the moon, where g is 1/6 the g of the earth, what force will it take to hold the box up?

A)  100N            B)  600N            C)  3600N          D)  0N

21.    I throw a ball upward with a speed of 20m/s.  If air resistance is negligible, what will its velocity be 2s later?

        A)  40m/s upward

        B)  40m/s downward

        C)  20m/s upward

        D)  20m/s downward

        E)  0 m/s

22.     A car accelerates in a straight line from rest to a speed of 10 m/s in 10 s, moving 40 m in that time.  Its average speed was

A)  10 m/s         B)  5 m/s                    C)  4 m/s            D)  1m/s

23.    An object is dropped from rest and falls in the earth’s atmosphere, i.e. don’t neglect air resistance.  As it falls its

A)  the magnitude of its acceleration increases

B) speed decreases

C) the magnitude of its acceleration decreases

D) the magnitude of its acceleration stays at 10m/s2

24.    An object is moving west with a speed of 3m/s.  10s later it is moving east with a speed of 1m/s.  Its average acceleration was

        A)  0.4m/s2 East                  B)  0.2 m/s2 West                C)  10 m/s2 down

        D)  0.4m/s2 West                 E)  0.2 m/s2  East

25.    A 2kg has a velocity of 8m/s.  What magnitude of impulse will be required to reduce its velocity to 4m/s?

A)  4kgm/s         B)  8kgm/s         C)  16kgm/s                D)  24kgm/s

Short Answer:  6 points each.  Answer ALL five questions.

1.      Three horizontal forces are acting on the 20kg box at the right in the directions shown by the arrows.  One of the forces is unknown, the one with arrows on both ends.  The box has an acceleration of 0.5m/s2 to the left.

a)      What is the net force on the box?  (Be sure to indicate the direction.)

b)     Find the unknown force.  (Be sure to indicate the direction.)

 

 

2.      Consider the two masses at the right sliding across a level, frictionless surface.  The 4kg mass has a speed of 2m/s to the left.  The 2kg mass has a speed of 5m/s to the right.  ((Indicate the magnitude & direction of the quantities below.)

A)     What is the total momentum of the system consisting of the two masses? 

B)     If they collide, what will the total momentum be after the collision?

C)     If they stick together after the collision, what is their velocity? 

 

3.      What are mass and weight and what does each measure?

 

4.      Explain the concept of terminal velocity, i.e. what is it and what causes it.  Use the example of a ping-pong ball thrown off the roof of this building.

 

5.      Why do all objects in freefall near the earth’s surface experience the same acceleration?

 

Formulas

 

 

 

Change in Position = Final Position – Initial Position,             

 

1N = 1kgm/s2

 

 

VA relative to C = VA relative to B  + VB relative to C