Conceptual Questions

  1. An elevator suspended by a cable is descending at constant velocity. How many force vectors would be shown on a free-body diagram? Name them.

  2. A compressed spring is pushing a block across a rough horizontal table. How many force vectors would be shown on a free-body diagram? Name them.

  3. A brick is falling from the roof of a three-story building. How many force vectors would be shown on a free-body diagram? Name them.

  4. In FIGURE Q5.4, block B is falling and dragging block A across a table. How many force vectors would be shown on a free-body diagram of block A? Name them.

    FIGURE Q5.4

    The figure illustrates two blocks labeled "A" and B connected by a rope. Block "A" is on a horizontal surface. The rope passes over a pulley attached diagonally to the right corner of a horizontal surface. Block B hangs from the rope.

  5. You toss a ball straight up in the air. Immediately after you let go of it, what force or forces are acting on the ball? For each force you name, (a) state whether it is a contact force or a long-range force and (b) identify the agent of the force.

  6. A constant force applied to A causes A to accelerate at 5 m/s2. The same force applied to B causes an acceleration of 3 m/s2. Applied to C, it causes an acceleration of 8 m/s2.

    1. Which object has the largest mass? Explain.

    2. Which object has the smallest mass?

    3. What is the ratio mA/mB  of the mass of A to the mass of B?

  7. An object experiencing a constant force accelerates at 10 m/s2. What will the acceleration of this object be if

    1. The force is doubled? Explain.

    2. The mass is doubled?

    3. The force is doubled and the mass is doubled?

  8. An object experiencing a constant force accelerates at 8 m/s2. What will the acceleration of this object be if

    1. The force is halved? Explain.

    2. The mass is halved?

    3. The force is halved and the mass is halved?

  9. If an object is at rest, can you conclude that there are no forces acting on it? Explain.

  10. If a force is exerted on an object, is it possible for that object to be moving with constant velocity? Explain.

  11. Is the statement “An object always moves in the direction of the net force acting on it” true or false? Explain.

  12. Newton’s second law says F⃗net=ma⃗. So is ma⃗ a force? Explain.

  13. Is it possible for the friction force on an object to be in the direction of motion? If so, give an example. If not, why not?

  14. Suppose you press your physics book against a wall hard enough to keep it from moving. Does the friction force on the book point (a) into the wall, (b) out of the wall, (c) up, (d) down, or (e) is there no friction force? Explain.

  15. FIGURE Q5.15 shows a hollow tube forming three-quarters of a circle. It is lying flat on a table. A ball is shot through the tube at high speed. As the ball emerges from the other end, does it follow path A, path B, or path C? Explain.

    FIGURE Q5.15

    The figure illustrates the top view of a hollow tube that is trimmed at the top and at the right center.

  16. Which, if either, of the basketballs in FIGURE Q5.16 are in equilibrium? Explain.

    FIGURE Q5.16

    The figure illustrates the forces acting on two basketballs. A dot is marked at the center of the basketballs.

  17. Which of the following are inertial reference frames? Explain.

    1. A car driving at steady speed on a straight and level road.

    2. A car driving at steady speed up a 10° incline.

    3. A car speeding up after leaving a stop sign.

    4. A car driving at steady speed around a curve.