GENERAL PHYSICS I EXAM 2 NAME_______________________________________

3] A block of mass 2.0 kg is observed to slide down an incline at a constant velocity when the incline makes an angle of 30 degrees with the horizontal. What is the coefficient of kinetic friction between the block and incline?
        ANSW: 0.58

EXPLAIN BRIEFLY which one of Newtonís three laws of motion BEST describes the above situation {Credit will be given only if an explanation is included!} NOTE: All 3 laws can be applied here but ONE will best describe the state of this object.
 
 

4] A mass of 0.50 kg is hanging vertically by a string. It is known that the string will break if the tension in it exceeds 25 N. What is the maximum acceleration that can be given to the mass by pulling up on the string?

ANSW: 40 m/s/s

     Describe the condition(s) that would be required for the tension in the string to be equal to zero.
                                                 

4] You watch the following events happen while standing on the shore. Two sailing ships are passing your location. As you watch ship #1 pass by, moving at constant velocity, a stone is dropped from a tall mast of the ship and lands on its deck. Ship #2 passes by, moving with a constant acceleration, and a stone is also dropped from a tall mast landing on its deck. EXPLAIN, with reference to the appropriate laws of motion, where each stone (#1 and #2) lands relative to the mast from which it fell. {i.e., do they land at the foot of the mast or behind it?}
 

5] You are pulling a small child on a snow sled up a slope that makes a 30 degree angle with the horizontal . The combined mass of the child and sled is 20.0 kg. It is known that the coefficient of kinetic friction between the snow and sled is m k = 0.130 . If you pull the rope such that a constant force of 125 N is acting on the sled parallel to the surface of the slope, what is the acceleration of the sled/child combination up the incline?       

ANSW: +.245 m/s/s

1]     A 2.50 gm bullet passes through a material that is 1.25 cm thick. The bullet enters
        the material with a velocity of 350 m/s and exits the material with a velocity of 250 m/s.
        Find the work done on the bullet by friction as it passes through the material and the
        average force of friction on the bullet.

Answer: W(fric) = - 75.0 J F(fric) = 6000 N
 

2]     A 2.00 kg block sliding down a frictionless ramp has a velocity of 0.50 m/s when at a
        height , h , above a level surface. The block slides to the bottom of the ramp and continues
        to slide a short distance along a level (frictionless) surface until it comes to rest after
        compressing a spring a distance of 1.50 cm. The spring constant is k = 4.6 x 104 N/m.
        Find the height, h , for the block. {NOTE: the angle of the ramp and length of the ramp are
        unknown!}

Answer: 0.25 m

1]     A skier with a mass of 60.0 kg has a speed of 3.50 m/s when they are at a vertical height 24.0 m
        above the bottom of a hill. If a constant frictional force of 70.0 N opposes their motion down the
        hill and the length of the slope is 65.0 m, what is their speed at the bottom of the hill?

                Answer: 18.2 m/s
 

2]     A spring with spring constant k = 75.0 N/m is used to launch a projectile of mass 100 gm straight
        up. If the spring is compressed 12.5 cm in order to launch the projectile, how high above this
        compressed spring point is the projectile when it has a speed of +1.50 m/s? (Neglect friction for
        this problem!)

                Answer: 0.483 m

 

SAMPLE MULTIPLE CHOICE

1)  A packing crate slides down an inclined ramp at constant velocity.  Thus, we can deduce that
    a) a frictional force is acting on it.
    b) a net downward force is acting on it.
    c) it may be accelerating.
    d) it is not acted on by an appreciable gravitational force.

2)  When you sit in a chair, the sum of all the forces acting on you while you sit
    a) is up
    b) is down
    c) depends on your weight
    d) is zero

3)  If you blow up a balloon and then release it, the balloon will fly away.  This is an illustration of
    a) Newton's 1st law
    b) Newton's 2nd law
    c) Newton's 3rd law
    d) the law of gravity

4) A mass is suspended from the ceiling by means of a string.  The Earth pulls downward on the mass with the weight force
     of the mass equal to 8 N.  If this is the "action" force of the 3rd law, what is the "reaction" force?
    a) the string pulling upward on the mass with an 8 N force
    b) the ceiling pulling upward on the string with an 8 N force
    c) the string pulling downward on the ceiling with an  8 N force
    d) the mass pulling upward on the Earth with an 8 N force

5)  According to the scientific definition of work, pushing on a rock accomplishes no

     work unless there is

  A) an applied force greater than its weight.

  B) a net force greater than zero.

  C) an opposing force.

  D) movement in the same direction as the force.

 

6)   The potential energy of a box on a shelf, relative to the floor, is a measure of

  A) the work done putting the box on the shelf from the floor.

  B) the weight of the box times the distance above the floor.

  C) the energy the box has because of its position above the floor.

  D) any of these

 

7)   Which quantity has the greatest influence on the amount of kinetic energy that a large

       truck has while moving down the highway?

  A) mass

  B) weight

  C) velocity

  D) size

 

8)   The law of conservation of energy is a statement that

  A) energy must be conserved and you are breaking a law if you waste energy.

  B) the supply of energy is limited so we must conserve.

  C) the total amount of energy is constant.

  D) energy cannot be used faster than it is created.

 

 

 

 

SAMPLE MULTIPLE CHOICE QUESTIONS FOR MOTION AND NEWTON'S LAWS
ANSWERS

1)  a

2)      d

3)      c

4)      d

5)      d

6)      d

7)      c

8)      c