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Physics 101 Exam 1
8 October 2004 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 net force of 18 N acts on a block for 5 s. During that time, the block has an acceleration of 3 m/s$^2$. What is the mass of the block?





  2. A 1000-kg car travelling at 38 m/s East is seen entering a tunnel. Five seconds later it drives out of the tunnel travelling 27 m/s West.

    a) What was the change in velocity of the car during that time?

    b) What was the acceleration of the car during that time (give magnitude and direction)?









  3. You are travelling in a golfcart down the road at a speed of 10 m/s. You want to throw your full water bottle to your friend, who is standing still. You throw the water bottle as you pass your friend. Neglect air resistance. To make sure that she can catch it, you should aim your throw:

    = 1.4in \epsffile{golfcart.eps}

    1. at point A (behind your friend)
    2. at point B (at your friend)
    3. at point C (ahead of your friend)
    4. need more information






  4. You drive from Norfolk to Richmond. You travel 10 miles in the first hour, 60 miles in the second hour, and 50 miles in the third hour. What was your average speed?







  5. You are driving your car around a curve in a parking lot at about 15 mph. When you reach point A, you hit a large patch of oil and there is suddenly no friction between the tires and the road. Draw a line indicating your motion in the next second.

    = 2in \epsffile{curve.eps}

  6. A 4 kg pumpkin is dropped from the 10th floor of a building and hits the ground with a certain speed. Neglect air resistance. If you want the pumpkin to hit the ground with half the speed, 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 20 m from a tree. How much time did it take to fall?





  8. A 1000-kg car is driving down the highway in a straight line at a constant speed of 30 m/s (65 mph). The only horizontal forces on the car are the force due to the engine, the force of friction, and the force of air resistance. The engine of the car applies a force of 1500 N in the direction of travel. What is the total force of air resistance plus friction on the car?

    1. 0 N
    2. between 0 and 1500 N
    3. 1500 N
    4. more than 1500 N
    5. need more information






  9. I throw a 0.5 kg ball straight down from a 1000-m high balloon at a speed of 20 m/s. Two seconds later, what are (a) the velocity and (b) the acceleration of the ball?







  10. On Earth, a 1000-kg Honda Civic can go from 0 to 60 mph in 8 sec. Suppose that the Civic is moved to a planet where the gravitational field is twice as strong (so that $g_{planet} = 20$ m/s$^2$). Assume that the engine can exert the same force on this planet as on Earth. How much time will it take to accelerate from 0 to 60 mph?

    1. 2 sec
    2. 4 sec
    3. 8 sec
    4. 16 sec
    5. 32 sec
    6. Not enough information






  11. A 1000-kg Civic going 45 miles per hour on dry roads applies the brakes and stops in a period of time $t$. If instead the road is wet 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






  12. (No explanation needed) You turn a fan and it blows air at you. If the fan pushing on the air is the action force, what is the reaction force?

    1. gravity pulling on the air
    2. the air pushing on you
    3. the air pushing on the fan
    4. gravity pulling on the fan
    5. gravity pulling on you
    6. Other
    7. Not enough information

  13. A small 50-kg (110 lb) hockey fan climbs onto the ice and is hit by a large 100-kg (220 lb) ice hockey player travelling at 12 m/s (25 mph) to the right. Assume that the hockey fan was not moving before he was hit and that the fan and the player are all tangled together after they hit.

    Which exerts more force on the other during the collision?

    1. The big hockey player exerts more force on the small hockey fan
    2. The small hockey fan exerts more force on the big hockey player
    3. Both exert the same force on each other
    4. Not enough information






  14. In the previous problem, what is the speed of the two tangled people immediately after the collision ? Ignore friction.

    1. more than 12 m/s
    2. 12 m/s
    3. less than 12 m/s but not zero
    4. zero
    5. Not enough information






  15. In the previous problem, which person has the greater change in velocity?

    1. The big player
    2. The small fan
    3. Both the same
    4. Not enough information






  16. In the previous problem, which person has the greater change in momentum?

    1. The big player
    2. The small fan
    3. Both the same
    4. Not enough information






  17. A 0.15 kg baseball travelling at 30 m/s toward the batter is hit by a baseball bat and then has a velocity of 25 m/s away from the batter. What was the force applied to the baseball by the baseball bat (in Newtons)?

    1. 0.75
    2. 1.5
    3. 5
    4. 8.25
    5. 55
    6. other
    7. Not enough information






  18. You throw a 1-kg rock straight upward at a speed of 20 m/s. What is the net force on the rock when it is half way to the top of its path? Ignore air resistance.





  19. Consider a person standing in an elevator that is accelerating upward. The upward normal force $N$ exerted by the elevator floor on the person is

    1. more than the person's weight
    2. equal to the person's weight
    3. less than the person's weight
    4. Not enough information







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2004-10-12