exam 2 ch6-10

A wrench is used to tighten a nut as shown in the figure. A 12-N force is applied 7.0 m from the axis of rotation. What is the magnitude of the torque due to the applied force?

84 N.m

The kinetic energy of a car is 8 x10^6J as it travels along a horizontal road. How much power is required to stop the car in 10 s?

8x 10^5 w

The angular displacement is measured in radian. What is the main advantages of using the radian

The radian is a ratio between two length scale (unitless), so there is no effect on other units when multiplying or dividing by the radian

An object of mass 4m, initially at rest, explodes breaking into two fragments of mass m and 3m, respectively. Which one of the following statements concerning the fragments after the explosion is true?

The smaller fragment will have three times the speed of the larger fragment.

A collision between two objects is elastic. Which one of the following statements concerning this situation is true?

The total kinetic energy of the objects is the same before and after the collision.

During a certain process, the linear momentum of a system is conserved. Which one of the following statements concerning this system is correct?

The vector sum of the average external forces acting on the system is equal to zero newtons.

Which one of the following is the SI unit for angular acceleration

radians per square second (rad/s2)

The moment of inertia of a wheel about its axle does not depend on which one of the following properties?

the angular velocity of the wheel as it rotates

A force that acts on an object is said to be conservative if

the work it does on the object is independent of the path of the motion

A man and boy are balancing each other standing at two sides of a wooden plank, supported by a fulcrum as shown in the figure. The man has a mass of 80 kg. Ignoring the weight of the wooden plank, find out the mass of the boy?

• 20 kg

Some What is the tangential speed of Nairobi, Kenya, a city near the equator? The earth makes one revolution every 23.93 h and has an equatorial radius of 6380 km.

• 465 m/s

2.0-kg ball has a velocity of 12 m/s downward just before it strikes the ground and bounces up with a velocity of 12 m/s upward. What is the change in momentum of the ball?

• 48 kg. m/s. upward

Which force below does the most work? All three displacements are the same. Given that Sin 60°=0.87 and Cos 60°-0.50 10N, 8N, 6N

• The 6 N force

Two solid spheres have the same mass, but one is made from lead and the other from wood. How do the moments of inertia of the two spheres compare?

The moment of inertia of the wood sphere is greater than that of the one made of lead.

40-kg block is vertically lifted 20 meters from the surface of the earth. To one significant figure, what is the change in the gravitational potential energy of the block?

+8000 J

A 66-N. m torque acts on a wheel with a moment of inertia 17.5 kg. m2, If the wheel starts from rest. how long will it take the wheel to make one revolution?

1.82 s

A drill bit in a hand drill is turning at 1200 revolutions per minute (1200 rpm). Express this angular speed in radians per second (rad/s).

126 rad/s

How much energy is dissipated in braking a 1000-kg car to a stop from an initial speed of 20 m/s?

200,000 J

Rank in order, from largest to smallest, the gravitational potential energies of the balls?

3 > 2 = 4>1

A projectile is launched with 200 kg x m/s of momentum and 500 J of kinetic energy. What is the mass of the projectile?

40 kg

The angles are measured either in degree or radian. One radian is equivalent to how much in degree?

57.3

As the name implies, the impulse-momentum theorem provides a relationship between impulse and momentum. Which one of the following statements correctly describes that relationship?

An impulse is equal to the change in an object's momentum that occurs when a net force acts on it.

Two points are located on a rigid wheel that is rotating with a decreasing angular velocity about a fixed axis. Point A is located on the rim of the wheel and point B is halfway between the rim and the axis. Which one of the following statements is true concerning this situation?

Both points have the same instantaneous angular velocity

The blades of a food processor (juice maker) has an angular acceleration of -3 rad/s?. Which one of the following statements is correct concerning this situation? (Assume counterclockwise rotation is positive.)

If the angular velocity is clockwise, then its magnitude must increase as time passes.

Which one of the following statements most accurately describes the center of gravity of an object?

It is the point from which the torque produced by the weight of the object can be calculated

In which one of the following circumstances does the force do positive work on the object?

The direction of the force is in the same direction as the object's displacement

Which one of the following statements concerning momentum is true?

Momentum and impulse are measured in the same units.

A circular disk of radius 0.015 m rotates with a constant angular speed of 5.0 rev/s. What is the acceleration of a point on the edge of the disk?

O 15 m/s2

In which one of the following situations is linear momentum not conserved?

O A tree limb is being struck by lightning and falls to the ground.

An object, which is considered a rigid body, is not in equilibrium. Which one of the following statements must be true concerning the magnitude of the angular acceleration a and translational acceleration a of the object?

O Either a > O rad/s or a >0 m/s

A rock is thrown straight up from the surface of the Earth. Which one of the following statements describes the energy transformation of the rock as it rises? Neglect air resistance.

O The kinetic energy decreases and the potential energy increases.

Which one of the following statements concerning the momentum of a system when the net force acting on the system has a positive value is true?

O The momentum of the system is increasing.

A force is applied to a doorknob. This force will be most effective in causing the door to rotate when which of the following is true?

The direction of the force is at an angle of 90° with respect to the door

Three objects are positioned along the x axis as follows: 4.4 kg at x = + 1.1 m, 3.7 kg at x = -0.80 m, and 2.9 kg at x = -1.6 m. The acceleration due to gravity is the same everywhere. What is the distance from the location of the center of gravity to the location of the center of mass for this system?

Zero meter

Which one of the following choices is produced when a constant net torque is applied to a rigid object ?

a change in the angular velocity of the object

In which one of the following situations is zero net work done?

a horse pulls a wagon at a constant velocity

The momentum of an object is not dependent on which one of the following quantities?

acceleration

The wheels of a race car moving without slipping as the car moves in a circular path at constant speed. Which one of the following quantities has a non-zero value and has a constant value in this situation?

angular velocity

During the summer vacation a student is helping his grand parents in putting new drywalls in the ceiling of the game room. The student used a drill to put screws into the drywall of the ceiling. The screws rotate clockwise as they go into the ceiling. What is the direction of the angular velocity of the screw as the drill drives it into the ceiling? Express the direction relative to the student, who is looking upward at the screw.

• up

Work may be expressed using all of the following units except:

•watt