Name: Honor Code Signature:
Physics 101 Exam 1
4 October 2002 Prof L. Weinstein

There are 16 problems. Please give a short explanation for all multiple choice questions. Show your work for all numerical answers.
 
 

  1. The Voyager 1 spacecraft was launched from the Earth in 1977 and is now 12.4 billion km from the Earth. What keeps the spacecraft going after the rocket no longer pushes it?

    2.  

     
     
     
     
     
     
     

  2. You are on a sailing ship traveling at a constant velocity of 5 m/s. You drop a 1 kg iron block from the top of the 20 m high mast. Where does the block land?


    3. = 1.2in\epsffile{boat.ps}

    1. 5 m in front of the mast
    2. at the base of the mast
    3. 5 m behind the mast
    4. 10 m behind the mast
    5. Not enough information
  3. For every force, there exists an equal and opposite force. Consider a rock dropped from a tall building. If the action force is that of the Earth pulling down on the rock, what is the reaction force?


    4. = 1.2in\epsffile{droprock.ps}
     
     
     
     
     

  4. A 1 kg rock is thrown straight upward with a speed of 30 m/s. Neglecting air resistance, what is the net force on the rock when it is halfway down from the top of its path?

    5.  

     
     
     
     
     
     
     

  5. A 350 lb football player and a 94 lb gymnast pull on opposite ends of a rope in a tug-of-war. Who exerts the greatest force on the rope?
    1. the football player
    2. the gymnast
    3. both forces are the same
    4. Not enough information

     
     
     
     
     
  6. You are looking down on a spiral tube from above as it sits on a flat table. A pellet is fired into the spiral tube at the arrow in the center. When it emerges, which path will it follow (ignore gravity)?


    7. = 2in\epsffile{spiral.eps}

    1. A
    2. B
    3. C
    4. Not enough information

     
     
     
     
     
  7. The Levi-Strauss trademark shows two horses trying to pull apart a pair of pants. Suppose that Levi had only one horse and attached the other side of the pants to a fencepost. Using only one horse would


    8. = 2in\epsffile{pullapart.ps}

    1. reduce the tension on the pants by one-half
    2. not change the tension on the pants
    3. double the tension on the pants
    4. other
    5. Not enough information
  8. You throw a 1.3 kg ball straight up in the air. It lands next to you 4 seconds later. Assume the ball spends half the time going up and the other half falling down. Ignore air resistance. How high did the ball go?

    9.  

     
     
     
     
     
     
     

  9. A 4000 kg truck going 30 miles per hour applies the brakes and stops in a certain amount of time. If you double the mass of the truck and the brakes apply the same amount of force, how much time will it take to stop?
    1. half as much
    2. the same
    3. twice as much
    4. four times as much
    5. Not enough information

     
     
     
     
     
  10. A 4000 kg truck going 30 miles per hour applies the brakes and stops in a certain amount of time. If the truck is travelling at 60 miles per hour and the brakes apply the same amount of force, how much time will it take to stop?
    1. half as much
    2. the same
    3. twice as much
    4. four times as much
    5. Not enough information

     
     
     
     
     
  11. A car rounds a curve while maintaining a constant speed. Is there a non-zero net force on the car as it rounds the curve?
    1. No
    2. Yes
    3. It depends on the sharpness of the curve and the speed of the car
    4. Not enough information

     
     
     
     
     
  12. An 83 kg batter hits a 150 g baseball travelling toward him at 40 m/s. After being hit, the ball is travelling at 35 m/s away from him. Assume that the impact took 0.002 seconds.


    13. a) What was the acceleration of the ball during the impact?
     
     
     

    b) What impulse did the ball exert on the bat during the impact?
     
     
     

    c) What force did the bat exert on the ball during the impact?
     
     
     
     
     
     
     

  13. An airplane flies 600 km in a straight line from Virginia Beach to New York City in 5 hours. What was its average speed? (Don't forget the units.)

    14.  

     
     
     
     
     
     
     

  14. A 727 airplane has a mass of 70 tons ($7\times 10^4$ kg). In an airplane pulling competition, teams of 20 people compete to pull the airplane a distance of 4 m. An average time is 10 s.


    15. a) What was the average speed of the airplane?
     
     
     

    b) Assume the maximum speed was twice the average speed. What was the acceleration of the airplane?
     
     
     

    c) What force did the team of people exert on the airplane?
     
     
     
     
      

  15. You are sliding along a frictionless icy pond at 6 m/s. You collide with a friend standing on the slippery ice and grab onto him. Your combined speed is now
    1. 0
    2. less than 6 m/s but more than 0
    3. 6 m/s
    4. more than 6 m/s but less than 10 m/s
    5. 10 m/s
    6. Not enough information

     
     
     
     
     
  16. In the previous problem, if your mass is 50 kg and his mass is 100 kg, what is your combined speed after the collision?

    17.  

     


2002-10-07