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Physics 101 Exam 1
6 October 2003 Prof L. Weinstein

There are 19 problems. Please give a short explanation for all multiple choice questions. Show your work for all numerical answers.

1. A force of 12 N acts on a 2-kg block for 3 s. What is the acceleration of the block during that time?
   
   
   
   
   
   

2. A 3-kg car travelling at 30 m/s East stops gradually in 6 s. What is the acceleration of the car (give magnitude and direction)?

   
   
   
   
   
   
   

3. Two trains are running on parallel train tracks, each at $v=30$ mph. You are on one train and your friend is on the other train. You throw a heavy object directly at your friend. Neglecting air resistance, it will land

   = 1.4in

   1. ahead of your friend
   2. at (next to) your friend
   3. behind your friend
   4. need more information
   
   
   
   
   
   
   

4. What is the average speed of a bicycle if it travels 5 m in the first second, 6 m in the next second, and 7 m in the third second?

   
   
   
   
   
   
   

5. A 3 kg block of ice travelling at a speed of 5 m/s on an icy surface is a attached to a ring by a 2m long string. The string keeps it moving in a horizontal circle. (The left side picture shows the view form the side, the right side picture shows the view from above.) If the string breaks suddenly, which path will the ice block follow?

   = 2in

   1. A
   2. B
   3. C
   4. D
   5. E
   6. need more information

6. A 4 kg pumpkin falls from the 2nd floor of a building and hits the ground a time $t$ later. If you want the pumpkin to take twice as long to hit the ground (ie: $2t$), you should drop it from a height
   1. 1/4 as high
   2. 1/3 as high
   3. 1/2 as high
   4. twice as high
   5. four times as high
   6. need more information
   
   
   
   
   
   
   

7. A 0.5 kg apple falls from a tree and hits the ground 2 sec later. What was the speed of the apple when it hit the ground?

   
   
   
   
   
   
   

8. I have three pieces of gold. One has a weight of 1 N on the Moon ($g = 1.6$ m/s$^2$). The second has a weight of 1 N on the Earth ($g = 10$ m/s$^2$). The third has a weight of 1 N on Jupiter ($g = 27$ m/s$^2$). Which piece has the greatest mass?
   1. The one on the Moon
   2. The one on the Earth
   3. The one on Jupiter
   4. need more information
   
   
   
   
   
   
   

9. The force of friction on a sliding 5 kg chair is 20 N. You push it across the room. How much force do you have to apply once it is moving in order to keep it moving at constant velocity?
   1. 0 N
   2. 10 N
   3. 20 N
   4. 50 N
   5. need more information
   
   
   
   
   
   
   

10. I throw a 0.2 kg apple straight up at a speed of 20 m/s. Two seconds later, what are (a) the velocity and (b) the acceleration of the apple?

    
    
    
    
    
    
    

11. A 1000 kg Honda Civic can go from 0 to 60 mph in 8 sec. When the driver slams on the brakes at 60 mph, it can stop in 4 sec. Which is true?
    1. The brakes can apply four times as much force on the car as the engine
    2. The brakes can apply twice as much force on the car as the engine
    3. The brakes can apply equally as much force on the car as the engine
    4. The brakes can apply half as much force on the car as the engine
    5. The brakes can apply one-fourth as much force on the car as the engine
    6. Not enough information
    
    
    
    
    
    
    

12. A 4000 kg truck going 30 miles per hour applies the brakes and stops in a period of time $t$. If instead the rear brakes fail so that the brakes only exert half as much force, how much time would it take to stop?
    1. one-fourth as much
    2. half as much
    3. the same
    4. twice as much
    5. four times as much
    6. Not enough information
    
    
    
    
    
    
    

13. A baseball player slides into homeplate. During the slide, the ground exerts a frictional force on the player that decreases her speed. If this frictional force is the action force, what is the reaction force?
    1. The force of gravity of the Earth on the player
    2. The normal force of the ground on the player
    3. The force of gravity of the player on the Earth
    4. The force of friction of the player on the ground
    5. Other
    6. Not enough information
    
    
    
    
    
    
    

14. A 2 ton (2000 kg) Ford Explorer travelling at 20 m/s to the right and a 1/2 ton (500 kg) Mini travelling at 20 m/s to the left collide head on and stick together.

    Which exerts more force on the other during the collision?

    = 0.8in

    1. The Explorer exerts more force on the Mini
    2. The Mini exerts more force on the Explorer
    3. Both exert the same force on each other
    4. Not enough information
    
    
    
    
    
    
    

15. In the previous problem, what is the speed of the wreckage immediately after the collision (ie: before friction makes them slide to a halt)?
    1. more than 20 m/s
    2. 20 m/s
    3. less than 20 m/s but not zero
    4. zero
    5. Not enough information
    
    
    
    
    
    
    

16. In the previous problem, in what direction is the wreckage moving immediately after the collision (ie: before friction makes them slide to a halt)?
    1. right
    2. left
    3. up
    4. down
    5. They are not moving
    6. Not enough information
    
    
    
    
    
    
    

17. In the previous problem, which car has the greater change in velocity?
    1. The Explorer
    2. The Mini
    3. Both the same
    4. Not enough information
    
    
    
    
    
    
    

18. In the previous problem, which car has the greater change in momentum?
    1. The Explorer
    2. The Mini
    3. Both the same
    4. Not enough information
    
    
    
    
    
    
    

19. A 1 kg flowerpot falls 5 m onto the ground and shatters. What force did the flowerpot exert on the ground?
    1. 1 N
    2. 5 N
    3. 10 N
    4. 100 N
    5. Other
    6. Not enough information