Midterm Exam 1:   Essentials of Physics-- PHYS 101

25 April, 2007

This exam consists of 16 multiple choice questions (worth 2 points each).  Please put your name on the Scantron form and indicate your answers to the multiple choice questions on it.  Important formulae and conversion factors can be found on the last page.

_53_1) If you have snow on your boots, you can get the snow off by stamping your boots on the floor. This is in accord with the law of

A)  inertia.

B)  tension.

C)  conservation.

D)  equilibrium.

E)  action and reaction.

_50_2) A hockey puck is set in motion across a frozen pond.  If ice friction and air resistance are neglected, the force required to keep the puck sliding at constant velocity is:

A)  equal to the weight of the puck.

B)  the weight of the puck divided by the mass of the puck.

C)  zero Newtons.

D)  the mass of the puck multiplied by 9.8 m/s/s.

E)  none of these.

_84_3) You have two cars.  You push on the second with double the net force of the first and they both are observed to accelerate the same.  What is a correct explanation?

A)  The second cart experiences friction that the first cart didnÕt.

B)  The mass of the second cart is double that of the first.

C)  The mass of the second cart is half that of the first.

D)  Air resistance was more for the second cart.

_24_4) You are bicycling down a flat road.  While maintaining a constant speed, you change gears so that you are cranking the pedals faster.  Your speed, air resistance and friction donÕt change.  During this, the work you are exerting on the bicycle:

A)  is less, as you are exerting less force over the same distance.

B)  is less, as you are exerting less force over less distance.

C)  is the same, as you are exerting the same force over the same distance.

D)  is the same, as you are exerting less force over a greater distance.

E)  is more, as you are exerting less force but over an even greater distance.

 

Answer is C, 61% were correct.

_18_6) If you push an object twice as long (in time) while applying the same force you do:

A)  half as much work.

B)  twice as much work

C)  the same amount of work.

D)  not enough information is given to know.

_79_7) During the lab session you timed yourself running up a flight of stairs to determine your "personal power rating."  You did this by calculating the gravitational potential energy (GPE) you gained in running up the stairs and dividing it by the time it took.  Three months, four milkshakes a day and an extra 20 lbs later, you undertake a similar experiment.  To your surprise, you find that your personal power rating is unchanged.  Which of the following correctly explains this result.

A)  The GPE you gained is the same and the time required to run up the stairs was the same.

B)  The GPE you gained is more, but the time required to run up the stairs is less.

C)  The GPE you gained is less, but the time required to run up the stairs is also less.

D)  The GPE you gained is more, but the time required to run up the stairs is the same.

E)  The GPE you gained is more and the time required to run up the stairs is more.

_58_8) As you are leaping into the air, how does the force that you exert on the ground compare with your weight?  Why?  Choose the best answer and explanation below.  (hint: think of doing this experiment on a bathroom scale).

A)  It must be greater than your weight.  The floor pushes back with a force equal to your weight and you fly upwards.

B)  It must be greater than your weight.  The floor pushes back with an equal force, which is greater than your weight.

C)  It must be equal to your weight.  Then the floor pushes back on you with a greater force and pushes you upwards.

D)  It must be equal to your weight.  The floor pushes back with an equal force upwards, which propels you upwards.

E)  It must be less than your weight.  Since it is less than your weight the force with which the floor pushes back on you is greater than your weight, and you go up.

_76_9) You have the curves (A -> D) at right on a graph, but you forgot to label the axes.  One curve was the result of an experiment where acceleration vs. mass was graphed when force is held constant (as was at the end of lab 2).  Which curve was it?

A)         B)        C)        D)

 

42_10) A ball with mass, m, is tossed upwards towards a motion detector.  The ball doesn't reach the motion detector, and finally falls to the ground (note: as usual, up is the positive direction).  Which of the following pairs of velocity/acceleration plots is consistent with the entire motion of the ball after release?  (Answer is: D)

66_11) Consider molecules of hydrogen gas and heavier molecules of oxygen gas that have the same kinetic energy. The molecules with more speed are

A)  oxygen.

B)  hydrogen.

C)  Both have about the same speed.

D)  Not enough information to determine.

11_12) When an object falls through the air, its velocity increases and its acceleration:

A)  decreases.

B)  stays the same.

C)  increases.

72_13) An object falls until it reaches terminal velocity.  After it is dropped, but before it reaches terminal velocity

A)  the force of gravity is decreasing, and the force of air resistance is constant.

B)  the force of gravity is decreasing, while the force of air resistance is increasing.

C)  the force of gravity is constant, and so is the force of air resistance.

D)  the force of gravity is constant, and the force of air resistance is increasing.

E)  the force of gravity is constant, and the force of air resistance is decreasing.

21_14) A 1-kg ball is thrown at 10 m/s straight upward. Neglecting air resistance, the net force that acts on the ball when it is halfway to the top of its path is about

A)  ½ N

B)  1 N

C)  5N

D)  7.5N

E)  10N

90_15) A ball is thrown upwards and returns to the same position. Compared with its original speed after release, its speed when it returns is about

A)  half as much.

B)  the same.

C)  twice as much.

D) four times as much.

58_16) Your weight is

A)  equal to your mass.

B)  the gravitational attraction force between you and the Earth.

C)  a property of mechanical equilibrium.

D)  all of these.

Important formulae and conversion factors

 

Linear Motion

Circular Motion

velocity:          

{m/s}(y=position, t=time)

angular velocity:         

(q=angular position in radians)

acceleration:     {m/s2}

(v=velocity, t=time)

angular acceleration: 

{radians/s2}

inertia:             mass (kg)

(Òresistance to change in motionÓ)

rotational inertia:          I (kg m2)

(I=moment of inertia, the Òresistance to change in rotationÓ)

Newton's Second Law:           SF = m a

(SF=sum of forces, m=mass, a=acceleration)

NewtonÕs Second Law:        St = I a

(St=sum of torques, a=angular acceleration)

 

Newton's First Law:    SF = 0             an object in motion or standing still will continue in the same motion (or standing still) if no forces are applied to it.

 

NewtonÕs Third Law:              For every action there is an equal an opposite reaction

 

Definition of Energy:              "Energy is the capacity to do work."

 

Work:              Work = Force x displacement          {N x m}  (force and disp. in same direction)

 

Gravitational Potential Energy (GPE):           

 

                        GPE = m g h {J}       (g=acceleration of gravity, h=height)

 

Kinetic Energy (KE):

 

                        KE = 1/2 m v2 {J}      (v=velocity)

 

Power: (P):

 

P = work / time (W)

 

Angular Momentum:

 

                        Angular momentum = m v r (kg m2 / s)

 

Universal Law of Gravity:

 

                        F = G m1 m2 / d2  (N)

 

 

Conversion Factors, Constants and etc:

 

"kg" = kilogram          1 kg = 1000 g (grams)                        1 kg = 2.2 lb (lb is really unit of force!)

 

"m" = meter                 1000m = 1km (kilometer)       1600m = 1 mile

 

g = 9.8 m/s2  (about 10 m/s2)   (acceleration due to gravity at Earth's surface)

 

"N" = Newton = 1kg m /s2  (force unit)          1 lb = 4.45 N

 

"J" = Joule = 1 kg m2 / s2 (energy unit)           1 cal (calorie) = 4.2J    1Cal (kilocalorie) = 1000cal

 

"W" = Watt = 1 J / s (power unit)       1 kW (kilowatt) = 1000W