Physics Final

Question 1

Rotational inertia (or moment of inertia) depends on an objects mass and its
A. Rotational speed
B. Weight
C. Distribution of mass, as Julius Sumner muller would say
D. Torque

Answer 1

C. Distribution of mass

Question 2

In the video we saw of professor Julius Summer, he was delighted to show us that all disks beat all hoops. What equation could you use to find the speed of a disk after rolling from rest down a ramp of vertical height h?
A. rF= Ia 
B. mgh=1/2mv^2
C. mgh= 1/2mv^2+1/2Iw^2
D. mgh+1/2mvo^2+1/2Iw^2=1/2mv^2+1/2Iw^2

Answer 2

C. mgh=1/2mv^2+1/2Iw^2

Question 3

What is the quantity used to measure an objects resistance to changes in rotational motion?
A. Mass
B. Moment of inertia 
C. Torque
D. Angular velocity 
E. angular acceleration

Answer 3

B. Moment of inertia

Question 4

A man is holding an 8.00 kg vacuum leaner at arms length, a distance of .550 m from his shoulder. What is the torque on the shoulder joint of the arm is horizontal? Hint: T=rF
A. .242 Nm
B. 4.40 Nm
C. 43.2 Nm
D. 14.5 Nm
E. 0 Nm

Answer 4

C. 43.2 Nm

Question 5

A 15 kg child is sitting in a playground teeter totter, 1.5 m from the pivot. What is the minimum distance, on the other side of the pivot, such that a 220 N force will make the child lift off the ground?
A. 1 m
B. 1.5 m
C. .102m
D. 9.78 m
E. 2.35 m

Answer 5

A. 1 m

Question 6

A mass of 375 g hangs from a string that is wrapped around the circumference of a pulley with s moment of inertia or .0125 kgm^2 and a radius of 26 cm. When the mass is released, the mass accelerated downward and the pulley rotates about its axis as the string unwinds. What is the acceleration of the mass? 
A. 19.9 m/s^2              Hint: T-mg=ma
B. 15.8 m/s^2
C. 13.1 m/s^2
D. 6.57 m/s^2
E. 3.27 m/s^2

Answer 6

D. 6.57 m/s^2

Question 7

The torque required to turn the crank on an ice cream maker is 4.5 Nm. How much work does it take to tune the crank through 300 full turns?
A. 4240 J
B. 7480 J            Hint:W=Tdeltatheta 
C. 2120 J
D. 1350 J
E. 2700 J

Answer 7

B. 8480 J

Question 8

A 5 m radius playground merry-go-round with a moment of inertia of 2000 kgm^2 is rotating freely with an angular speed of 1 rad/s. Two people, each having a mass of 60 kg are standing right outside the edge of the merry-go-round and step on it with negligible speed. What is the angular speed of the merry-go-round right after the two people have stepped on. Iwf=Iwi
A. .2 rad/s
B. .4 rad/s
C. .6 rad/s

Answer 8

B. .4 rad/s

Question 9

The planet Venus has a very nearly the same size and mass as the earth, but it's distance from the sun is about 2/3 of the earths distance. What can you say about the force of the sun on Venus, as compared with the force of the sun on the earth? The force of the sun on feud is about \_\_\_\_\_\_ of the force of the sun on the earth.
A. 2/3
B. 4/9
C. 3/2 
D. 9/4

Answer 9

D. 9/4

Question 10

If we double the mass, what will happen to the period of the motion?
A. It will not change
B. It will increase by a factor of the square root of two, if 1.41
C. It will double
D. It will decrease to half its previous value

Answer 10

B. It will increase by a factor of the square root of two, or 1.41

Question 11

For a periodic process, the number of cycles per unit time is called the 
A. Amplitude
B. Wavelength 
C. Frequency 
D. Period
E. energy

Answer 11

C. Frequency

Question 12

Both pendulum A and B are 3 m long. The period of A is T. Pendulum A is twice as heavy as pendulum B. What is the period of B?
A. .71T
B. T
C. 1.4T
D. 2T
E. 3T

Answer 12

B. T

Question 13

If you look carefully at a grandfather clock, you will notice that the weight at the bottom of the pendulum can be moved up or down by turning a small screw. Suppose you have a grandfather clock at home that runs slow. What should you do?
A. Leave it alone, the period of a pendulum is independent of length
B. Turn the screw to raise the weight and shorten the pendulum
C. Turn the crew to lover the weight and lengthen the pendulum
D. Leave the screw alone but attached extra mass to the pendulum weight.

Answer 13

B. Turn the screw to raise the weight and shorten the pendulum

Question 14

An ice skater doing a spin pulls in her arms, decreasing her moment of inertia by a factor of two. How does her angular speed change?
A. It is reduced by a factor of 2
B. It is reduced by a factor of 4
C. It increase by a factor of 2
D. It increases by a factor of 4
E. it doesn't change

Answer 14

C. It increases by a factor of 2

Question 15

An object is moving in a circular path with an angular speed of 1.52 rad/s. How long does it take the object to complete one revolution?
A. 4.13 s
B. 2.07 s
C. 118 s
D. 4.77 s
E. 8.26 s

Answer 15

A. 4.13 s

Question 16

Angular momentum cannot be conserved if 
A. The angular acceleration changes 
B. The angular velocity changes 
C. There is a net force on the system 
D. The moment of inertia changes 
E. the net torque is not zero

Answer 16

E. the net torque is not zero

Question 17

A magnetic disk in a computer hard drive starts from rest when the computer is turned on and reaches a speed of 7200 rev/m after 3 seconds. What is its angular acceleration?
A. 1.05 rad/s
B. 250 rad/s
C. 240 rad/s
D. 22,900 rad/s

Answer 17

B. 250 rad/s

Question 18

The gravitational force between two objects is inversely proportional to
A. The distance between the two objects
B. The square of the distance between the two objects
C. The product of the masses of the two objects
D. The square of the product of the masses of the two objects
E. none of the above

Answer 18

B. The square of the distance between the two objects