Physics 101
		Exam 1 Sample
		  Solutions

A.1: C
     A theory, like the theory of gravity or the theory of evolution,
     synthesizes a tremendous amount of data and makes predictions of
     what we will find in the future.

A.2: C
     gravity is gravity

A.3: C
     There are no horizontal forces acting on the package so its
     horizontal velocity will not change.

A.4: D
     The average speed of the car was 50 mph but we do not know if the
     driver stopped for a 2 hour lunch and drove the rest of the time
     at 100 mph.  Maybe he stopped for a 3 hour lunch and drove the
     last hour at 200 mph.  We don't know.

A.5: A
     Constant velocity means zero acceleration.  Period.  If you drive
     at 100 km/h (about 60 mi/h) for 10 seconds, 10 minutes or 10
     hours, you are still driving at constant velocity for that period
     of time.

A.6: C
     Gravity makes your downward speed increase every second.  That
     means that every second you cover a longer distance than the
     preceding second.  The larger the gravitational acceleration, the
     faster your velocity and distance traveled increase.

A.7: D
     In one second, the object's downward velocity increases by 10 m/s
     (since g = 10 m/s^2 downward).  This means that v = 50 m/s down
     plus 10 m/s down = 60 m/s down.

A.8: d = 1/2 gt^2 = 1/2 * 10 m/s^2 * (6 s)^2 = 180 m

A.9: A
     definition of inertia

A.10: A
      F = ma.  The mass is the same so the required force to
      accelerate it is the same.  (The force of gravity on the car
      would be less so it would hurt less if it ran over your foot.)

A.11: A
      vectors have magnitude  and direction
      a force does not _have_ mass and acceleration
      a force does not have action and reaction components

A.12: C
      gravity exerts a force of 10 N down
      air resistance exerts a force of 4 N up
      the net force is 10 N down + 4 N up = 6 N down

A.13: A
      If it is at rest, then there is no acceleration and zero net
      force.

A.14: A
      F=ma.  If you decrease F, then you will decrease a.
      This is why they don't put Mini or Escort engines in Corvettes.

A.15: B
      The acceleration with the original engine is 
      a = delta v / t = 60 mi/h / 6 s = 10 mi/(h s)
      The new engine will deliver half the force, so using F=ma, it
      will produce half the acceleration.  Therefore a = 5 mi/(h s).
      (This means that the speed can increase by 5 mi/h each second or
      that it will take 12 s to go from 0 to 60 mi/h.)

A.16: C
      F=ma.  If you increase the mass by 10, you will need to increase
      the force by 10 to get the same acceleration.  (You can try this
      numerically by using an acceleration of 1 m/s^2 and see what
      size forces you need.)

A.17: a = delta v / t = 10 m/s / 2 s = 5 m/s^2
      F = m a = 10 kg * 5 m/s^2 = 50 kg m/s^2 = 50 N

A.18: action = force of ball on glove
      reaction = force of glove on ball

A.19: B
      action = reaction.  Force of hand on board = force of board on
      hand.  Both are 3000 N.

A.20: I GOOFED!  B is the only correct answer.  Sorry.
      B

      To see if the wagon accelerates, we need to consider all of the
      forces on the wagon.  We do not care what forces the wagon
      exerts on other objects; those do not affect the motion of the
      wagon.  The force of the wagon on the horse affects the horse,
      not the wagon.

      The net force on the wagon is not zero.  The
      net force on the wagon is the total of the forces from the
      horse, the ground, and gravity.