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Chapter 8: 8-8MCQ (page 198)

If you used 1000 J of energy to throw a ball, would it travel faster if you threw the ball (ignoring air resistance)

(a) so that it was also rotating?

(b) so that it wasn't rotating?

(c) It makes no difference.

Short Answer

Expert verified

The correct option is (b).

Step by step solution

01

Rotational kinetic energy

The total kinetic energy is equal to the sum of rotational kinetic energy and translational kinetic energy.For this problem, you need a greater linear speed, i.e., the translational kinetic energy is large.

You use 1000 J energy to throw the ball.

02

Explanation

When you use 1000 J energy to throw a ball, the ball's total kinetic energy just after the throw is 1000 J. The ball travels faster, which means it has a greater linear kinetic energy.

For a greater linear speed, the translation energy of the ball is large, and the rotational kinetic energy is the minimum. Now, the minimum values should be zero when the ball is not rotating. Therefore, for the highest translational speed of the ball, it should not rotate.

Hence, option (b) is correct.

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Most popular questions from this chapter

A uniform rod of mass M and length l can pivot freely (i.e., we ignore friction) about a hinge attached to a wall, as in Fig. 8–63. The rod is held horizontally and then released. At the moment of release, determine (a) the angular acceleration of the rod, and (b) the linear acceleration of the tip of the rod. Assume that the force of gravity acts at the center of mass of the rod, as shown. [Hint: See Fig. 8–20g.]

Question:(II) Two masses,\({m_{\bf{A}}} = 32.0 kg\)and\({m_{\bf{B}}} = 38.0 kg\)are connected by a rope that hangs over a pulley (as in Fig. 8–54). The pulley is a uniform cylinder of radius\(R = 0.311 m\)and mass 3.1 kg. Initially\({m_{\bf{A}}}\)is on the ground and\({m_{\bf{B}}}\)rests 2.5 m above the ground. If the system is released, use conservation of energy to determine the speed of\({m_{\bf{B}}}\)just before it strikes the ground. Assume the pulley bearing is frictionless.

A large spool of rope rolls on the ground with the end of the rope lying on the top edge of the spool. A person grabs the end of the rope and walks a distance l, holding onto it, Fig. 8–64. The spool rolls behind the person without slipping. What length of rope unwinds from the spool? How far does the spool’s center of mass move?

A turntable of radius is turned by a circular rubber roller of radius in contact with it at their outer edges. What is the ratio of their angular velocities,\({\omega _1}/{\omega _2}\)?

A small mass m on a string is rotating without friction in a circle. The string is shortened by pulling it through the axis of rotation without any external torque, Fig. 8–39. What happens to the angular velocity of the object?

(a) It increases.

(b) It decreases.

(c) It remains the same.

FIGURE 8-39

Mis-Conceptual Questions 10 and 11.
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