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Newton's Second Law, Fnet = ma Practice Problems for AP Physics B & C

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By — McGraw-Hill Professional
Updated on Feb 10, 2011

Review the following concepts if necessary:

Problems

Multiple Choice:

  1. A 2.0–kg cart is given a shove up a long, smooth 30° incline. If the cart is traveling 8.0 m/s after the shove, how much time elapses until the cart returns to its initial position?
    1. 1.6 s
    2. 3.2 s
    3. 4.0 s
    4. 6.0 s
    5. 8.0 s
  2. A car slides up a frictionless inclined plane. How does the normal force of the incline on the car compare with the weight of the car?
    1. The normal force must be equal to the car's weight.
    2. The normal force must be less than the car's weight.
    3. The normal force must be greater than the car's weight.
    4. The normal force must be zero.
    5. The normal force could have any value relative to the car's weight.
  3. In the diagram above, a 1.0–kg cart and a 2.0–kg cart are connected by a rope. The spring scale reads 10 N. What is the tension in the rope connecting the two carts? Neglect any friction.
    1. 30 N
    2. 10 N
    3. 6.7 N
    4. 5.0 N
    5. 3.3 N
  4. The velocity–time graph above represents the motion of a 5–kg box. The only force applied to this box is a person pushing. Assuming that the box is moving to the right, what is the magnitude and direction of the force applied by the person pushing?
    1. 2.0 N, right
    2. 2.0 N, left
    3. 0.4 N, right
    4. 0.4 N, left
    5. 12.5 N, left

Free Response:

  1. A 2–kg block and a 5–kg block are connected as shown above. The coefficient of friction between the 5–kg block and the flat surface is μ = 0.2.
    1. Calculate the magnitude of the acceleration of the 5–kg block.
    2. Calculate the tension in the rope connecting the two blocks.
  2. Bert, Ernie, and Oscar are discussing the gas mileage of cars. Specifically, they are wondering whether a car gets better mileage on a city street or on a freeway. All agree (correctly) that the gas mileage of a car depends on the force that is produced by the car's engine—the car gets fewer miles per gallon if the engine must produce more force. Whose explanation is completely correct?
  3. Bert says: Gas mileage is better on the freeway. In town the car is always speeding up and slowing down because of the traffic lights, so because Fnet = ma and acceleration is large, the engine must produce a lot of force. However, on the freeway, the car moves with constant velocity, and acceleration is zero. So the engine produces no force, allowing for better gas mileage.

    Ernie says: Gas mileage is better in town. In town, the speed of the car is slower than the speed on the freeway. Acceleration is velocity divided by time, so the acceleration in town is smaller. Because Fnet = ma, then, the force of the engine is smaller in town giving better gas mileage.

    Oscar says: Gas mileage is better on the freeway. The force of the engine only has to be enough to equal the force of air resistance—the engine doesn't have to accelerate the car because the car maintains a constant speed. Whereas in town, the force of the engine must often be greater than the force of friction and air resistance in order to let the car speed up.

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