Home Chapter 9 Practice Questions

# Practice Questions

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This activity contains 25 questions.

## What condition or conditions are necessary for rotational equilibrium?

 where t is torque.

## What condition or conditions are necessary for translational equilibrium?

A heavy seesaw is out of balance. A lightweight girl sits on the end that is tilted downward, and a heavy boy sits on the other side so that the seesaw now balances. If the boy and girl both move forward so that they are one-half their original distance from the pivot point, what will happen to the seesaw?

 The side the boy is sitting on will now tilt downward. The side the girl is sitting on will once again tilt downward. Nothing. The seesaw will still be balanced. It is impossible to say without knowing the masses and the distances.

A force is applied to the end of a 2 m long uniform board weighing 50 N in order to keep it horizontal, while it pushes against a wall at the left. If the angle the force makes with the board is 30° in the direction shown, the applied force F is

 25 N 43.3 N 50 N 100 N

## A force is applied to the end of a 2 m long uniform board weighing 50 N in order to keep it horizontal, while it pushes against a wall at the left. What is the horizontal component of the wall force?

 25 N 43.3 N 50 N 100 N

A uniform rod has a weight of 40 N and a length of 1 m. It is hinged to a wall (at the left end), and held in a horizontal position by a vertical massless string (at the right end). What is the magnitude of the torque exerted by the string about a horizontal axis which passes through the hinge and is perpendicular to the rod?

 5 m*N 10 m*N 20 m*N 40 m*N

## A uniform rod has a weight of 40 N and a length of 1 m. It is hinged to a wall (at the left end), and held in a horizontal position by a vertical massless string (at the right end). What is the force in the string in the previous question?

 5 N 10 N 20 N 40 N

## A uniform rod has a weight of 40 N and a length of 1 m. It is hinged to a wall (at the left end), and held in a horizontal position by a vertical massless string (at the right end). What is the magnitude of the hinge force?

 5 N 10 N 20 N 40 N

A uniform rod has a weight of 40 N and a length of 1 m. It is hinged to a wall (at the left end), and held in a horizontal position by a vertical massless string (at the right end). If the string is let go, what will be the initial angular acceleration?

## In the figure below, five forces act on a massless rod free to pivot at Point P. Which force is producing a counter-clockwise torque about Point P?

 A B C D E

## The slope of the straight line shown on the graph is called the

 bulk modulus. Young's modulus. compressibility. spring constant.

## Region A in the above figure is called the

 compressibilty region. plastic region. elastic region. fraction region.

## The Region B in the figure in the previous limit is called the

 compressibilty region. plastic region. elastic region. fraction region.

## The Point C in the figure is clearly not the

 breaking point. proportional limit. elastic limit. All of the above could be correct.

## The Point D in the figure is called the

 rupture point. rupture limit. elastic limit. none of the above.

## A person with a mass of 80 kg hangs from a trapeze suspended by two elastic cords. The force-stretch properties of the cords are shown in the figure. How far do the cords stretch?

 3.2 cm 32 cm 1.6 cm 16 cm

A person with a mass of 80 kg hangs from a trapeze suspended by two elastic cords. The force-stretch properties of the cords are shown in the figure. If the cords are 10 meters long and made of Nylon (E = 5 x 109 N/m2), what is their diameter?

 .1 m .02 m .004 m .008 m

## A person with a mass of 80 kg hangs from a trapeze suspended by two elastic cords. The force-stretch properties of the cords are shown in the figure. If the nylon cords have a radius of 6 mm, what is their length?

 33 m 23 m 13 m 3 m

A person with a mass of 80 kg hangs from a trapeze suspended by two elastic cords. The force-stretch properties of the cords are shown in the figure. If a cord described by the figure has a cross sectional area of .79 square centimeters and is stretched a half of a centimeter when a certain force is applied, what is the stress on it?

 1580000 N/m2 0.0158 N/m2 158 N/m2 15800 N/m2

## The red circle in the above 'movie' represents a person on a ladder. In which frame is the force of friction between the ladder and the ground the least? (There is no friction with the wall.)

 A B C D

## The red circle in the above 'movie' represents a person on a ladder. At which points is the ladder most in danger of falling?

 A and D C and D A and B B and C

## The red circle in the above 'movie' represents a person on a ladder. When is the wall force equal in magnitude to the force of friction?

 A B C D All of them.

## The red circle in the above 'movie' represents a person on a ladder. When is the normal force from the ground a minimum?

 A B C D All of the above.

## The bottom of the ladder is 1.2 m from the wall. What is the magnitude of the torque from the wall force about an axis through the bottom of the ladder?

 4000 m*N 2000 m*N 600 m*N 200 m*N

## The bottom of the ladder is 1.2 m from the wall. What is the magnitude of the torque from the red weight 1/3 of the way up the ladder about an axis through the bottom of the ladder?

 4000 m*N 2000 m*N 600 m*N 200 m*N