Q: You release the flipper so that $$\tau_c is $$the only torque acting on the flipper. It swings back to its original position at $$\omega = 4$$ rad/s. What is the angular momentum of the flipper?

$$L = 3.4 \times 10$$^{-3}$$ kg m^2$/s

Question 1

A box of mass 2 kg starts at rest on a frictionless slope, 1 m above the ground, and slides down to the bottom, reaching a speed of 3.5 m/s. Which of the following is true about the system's energy?

Accepted Answer

Mechanical energy is conserved at 19.6 J.

Question 2

You push a box of mass m up an incline with coefficient of friction μ and speed v with constant velocity. The power exerted by friction is:

Accepted Answer

$$\mu mgv$$

Question 3

A 0.5 kg beetle sits at the center of a circular turntable of mass m = 1 kg and radius r = 1.2 m. The turntable rotates at an angular velocity of $$\omega = 2$$ rad/s. The beetle then moves to the outside radius of the turntable. What is the new angular velocity of the turntable?

Accepted Answer

$$1.33$$ rad/s

Question 4

A cyclist rides her bike 5 miles. If her wheels have radius 0.67 m, approximately how many revolutions does she make during this trip?

Accepted Answer

3,740 revolutions

Question 5

A 0.60-kg solid cylinder is rolling across a horizontal surface at a speed of 4.0 m/s. How much work is required to stop it?

Accepted Answer

$$9.6 J$$

Question 6

You want to put a 400-kg satellite into geosynchronous orbit over Neptune, which has mass $$M = 1.02 	imes 10$$^{26}$$ kg and radius R = 2.5$$ 	imes $$10^7$$ meters. If Neptune spins once every 16.1 hours, at what altitude should your satellite orbit the planet?

Accepted Answer

$$4.2 	imes 10^7$ m

Question 7

A ball falls from height h and bounces up to a maximum height of 0.8h. Which of the following best describes the mechanical energy lost?

Accepted Answer

$$0.36mgh$$

Question 8

A neutron scatters off a proton at rest. Which of the following is true about the final kinetic energy of the neutron?

Accepted Answer

It can be less than its initial kinetic energy.

Question 9

An ice skater pulls her arms in to spin faster. What physical principle explains this?

Accepted Answer

Conservation of angular momentum

Question 10

An empty bucket is hung from the ceiling with two wires at 50° and 70° angles. If the bucket has mass 1 kg, what is the tension in each wire?

Accepted Answer

$$T_1 = 5.1$ N, T_2$ = 4.6 N$$

Question 11

You slowly fill the bucket with sand. At one point, the tension on one wire reaches its maximum tension of 50 N and the wire breaks. Which wire breaks?

Accepted Answer

The wire at 50°

Question 12

What is the mass of the sand in the bucket when the wire at 50° breaks (max tension 50 N)?

Accepted Answer

$$m = 4.1 kg$$

Question 13

Two springs of stiffness $$k = 300 N/m $$are placed vertically on a tabletop. A textbook of mass 2.5 kg is placed across the two springs. By how much are the springs compressed from their equilibrium length?

Accepted Answer

$$\Delta x = 0.041 m$$

Question 14

If you pick the book up (allowing the springs to extend back to their equilibrium length) and lift it back up 1.5 m above the equilibrium length, what is the change in gravitational potential energy?

Accepted Answer

$$\Delta U = 36.8 J$$

Question 15

The true compression is 90% of the value you found previously. How much energy (in J) is lost to dissipative forces?

Accepted Answer

$$E_{lost} = 0.25 J$$

Question 16

A pinball machine flipper is a great example of rotational motion turning into translational motion. For a flipper of length $$l = 7 cm$$, the moment of inertia is $$I = 8.5 	imes 10$$^{-4}$$ kg m^2$. You use a force F$ in the y-direction to push the flipper back to angle $$	heta = \pi/6$$. What is the magnitude of the torque required to hold it there?

Accepted Answer

$$	au = Fl \sin 	heta$$

Question 17

If the torque provided by the axis of the flipper pushing it in the clockwise direction is 0.1 Nm, what is the magnitude of the force required to fix the flipper in a static equilibrium at $$	heta = \pi/6$$?

Accepted Answer

$$F = 2.0 N$$

Question 18

You release the flipper so that $$	au_c is $$the only torque acting on the flipper. It swings back to its original position at $$\omega = 4$$ rad/s. What is the angular momentum of the flipper?

Accepted Answer

$$L = 3.4 	imes 10$$^{-3}$$ kg m^2$/s

Question 19

Assume the collision with the pinball is elastic, and the pinball has mass $$m = 0.08 kg $$and radius $$r = 2 cm. $$What velocity does the pinball leave after the collision?

Accepted Answer

$$v = 1.7 m/s$$

Question 20

Find the change in kinetic energy of the flipper-pinball system during the collision.

Accepted Answer

$$\Delta KE = 0 J$$

General Physics I – Practice Midterm Exam 2 Study Guide

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