Smart book assignment chapter 6

The force acting on an object and the object's displacement are in the same direction. Select all of the following that are possible values for the work done on the object.

20 J 60 J

A box slides down a 6.00 m long incline. The incline is 20.0° above the horizontal. The box is released from rest. The coefficient of friction between the box and the incline is 0.200. What is its speed at the bottom of the incline?

4.25 m/s

If mechanical energy is conserved and the potential energy increases, then what happens to the kinetic energy?

It decreases

The force of magnitude 10 N acting on an object and the object's displacement of magnitude 3 m are perpendicular. What is the work done on the object by the force?

0 J

500 J of energy is transferred in 10 s. Calculate the average power.

50W

When we say that a quantity does not change during any physical process, we call that a ______________ law.

Conservation

Where does the energy removed by friction go?

Internal energy Kinetic energy of atoms and molecules

What does conservation of energy mean?

The total energy of the universe never changes.

In the presence of nonconservative forces, which of the following equations could be used?

Wnc = ΔK + ΔU

The conversion of energy into a disorganized form is called

dissipation

Select all of the following that correspond to the law of conservation of mechanical energy. The subscripts are f for final and i for initial.

ΔK + ΔU = 0 Kf + Uf = Ki + Ui

A marble is placed in a track at a height 4h and released. How fast is the ball going just before it hits the ground? Friction and air resistance are negligible.

√8gh

Hooke's law describes how the force depends on the stretching or compressing of a spring. Match the following components of Hooke's law with their meanings

- The force and displacement are in opposite directions.The force and displacement are in opposite directions. k Spring constant x Displacement from equilibrium

When doing energy problems, which of the following can be replaced with ΔU?

- Wcons

For a conservative force, if WA→B = +20 J, then what is WB→A?

-20 J

The force acting on an object and the object's displacement are in opposite directions. Select all of the following that are possible values for the work done on the object.

-60 J -20 J

An object of mass 10 kg moves in one direction at 10 m/s along one straight line for 10 seconds. What is the total work done on the object?

0 J

Rank the magnitude of the force exerted by the four springs below based on the given spring constants and displacements from equilibrium, with the largest magnitude at the top and the smallest at the bottom.

0.3m, 30N/m 0.6 10 -0.5 10 0, 400

For the four displacements listed below, rank the magnitude of the associated spring force, with the largest magnitude at the top and the smallest magnitude at the bottom. Assume all springs have the same spring constant.

0.6 -0.5 0.3 0

A spring is used to propel a toy car across the floor. If you wish to double the launch speed of the toy car, by what factor must you change the distance the spring is initially compressed?

2

Rank the escape speed for a planet of radius 2 x 106 m, given the possible planet masses listed below. List in order of decreasing escape speed with the largest escape speed listed at the top and the smallest at the bottom.

2x10^11 1x10^10 5x10^9

A box of mass 10 kg is given an initial velocity of 3.0 m/s. The coefficient of kinetic friction between the box and the ground is 0.15. Approximately how far does the box slide before it stops?

3.0 m

If the speed of an object increases from v to 2v, then how much total work is done?

3/2 mv2

Select all of the following that are possible values for kinetic energy.

30 J 0 J

The equation for a particular force as a function of position is Fx(x) = (5 N/m)x. How much work does this force do on a particle that moves from x = 0 m to x = 4 m?

40J

Rank the change in gravitational potential energy with the largest change in gravitational potential energy at the top and the smallest at the bottom. The mass of the object is the same in each case.

An object moves from the sea level to the top of a large mountain An object moves from sea level to 5m above sea level An object moves horizontally

Select all of the following that are correct descriptions of potential energy.

Due to an interaction Easily recovered Stored energy

Select all of the following quantities that are included in the definition of average power.

Elapsed time Energy transferred

Select all of the following forces that have a corresponding potential energy.

Elastic force Electric force Gravitational force Conservative force

Which of the following equations is correct?

Emech = K + U

True or false: Conservative forces can change mechanical energy.

False

A compressed spring is released, and as it expands, it propels an object horizontally that was initially stationary and touching the spring. Which quantities are needed to determine the kinetic energy of the object just as it loses contact with the spring?

Final elastic potential energy Initial elastic potential energy

Rank the following according to the mechanical energy with the largest mechanical energy at the top and the smallest at the bottom.

K= 100J, U= 100J K= 0J, U= 100J K= 0J, U= 0J K= 0J, U= -100J

Rank the total work with the largest at the top and the smallest at the bottom.

Kf =30J, Ki= 0J Kf= 30J, Ki= 10J Kf= 30 J, Ki= 40J

Select all of the following that are forms of macroscopic mechanical energy.

Kinetic and Potential

If the work done by the gravitational force is positive, then what is the change in gravitational potential energy?

Negative

What are the possible values of gravitational potential energy given by equation 6-27?

Negative Approximately zero

Rank the following according to the total work done, with the largest total work done at the top and the smallest at the bottom

Net Force=(10N, north), displacement=(10m,north) Net Force= (20N, north), displacement=(20m,east) Net Force= (30N, north), displacement=(30m,south

Which of the following statements is correct?

Potential energy depends on position.

Select all of the following that are fundamental forms of energy.

Rest Potential Kinetic

In Hooke's law, what does the symbol k mean?

Spring Constant

Select all of the following that are needed to determine the total work done on an object.

The direction of the net force The magnitude of the displacement The direction of the displacement The magnitude of the net force

Which of the following statements is true?

The magnitude of the spring force is directly proportional to the magnitude of the displacement.

An ideal rope-and-pulley system is used to lift a pallet of bricks. The advantage of an ideal rope-and-pulley system is that less force is required to lift the object than if it were lifted without mechanical aid. Which statement is correct?

The total work done is the same as it would be if the mechanical aid were not used.

A mass attached to a spring is displaced from equilibrium. Which statement is always true?

The work done by the spring force is negative.

According to equation 6-27, for two spherical objects, the gravitational potential energy depends on which of the following?

Their masses The distance between their centers

Compare the escape speed of Planet E to Planet X: the mass and radius of Planet E is twice that of Planet X.

They are the same.

Which quantities are identified by conservation laws?

Those that do not change with time

True or false: Kinetic energy is always positive or zero.

True

What are the symbol and SI units for potential energy?

U, joules

If a graph of force versus position is plotted, how is the work done by the force related to this graph?

Work is the area under the graph.

Which of the following equations is correct?

Wtotal = Wcons + Wnc

According to equation 6-27, when two objects are very far apart, approximately, how much gravitational potential energy do they have?

Zero

How much work is done by the gravitational force when an object moves horizontally?

Zero

You are pulling your kid brother in a wagon at a constant speed. What is the total work done on the wagon?

Zero

A ball is thrown straight up. What is its kinetic energy when it reaches its highest point? Select all that apply.

Zero Smallest possible

All potential energies have a ______________ force associated with them.

conservative

Which of the following are the SI units of work?

kg⋅m2/s2 joules (J)

A spring with spring constant k = 2000 N/m is compressed by 0.02 m. After the spring is released, with what initial speed does the spring propel an object of mass 0.2 kg horizontally?

2 m/s

Rank the escape speed for a planet of mass 2 x 1011 kg, given the planet radii listed below. List in order of increasing escape speed with the smallest escape speed listed at the top and the largest at the bottom.

2 x 10^8 5 x 10^6 2 x 10^4

If the work done by gravity from point A to point B is equal to 20 J, then how much work would be done by gravity from point A to point B along a longer, less steep route?

20 J

A 1.0 kg ball is launched into the air with an initial speed of 14 m/s at an unknown angle and follows a parabolic path. What is the kinetic energy of the ball at 5.0 m above its launching point if it is on its way down after passing through the peak of its motion?

49 J

An object that weighs 10 N is moved down and to the right along the entire length of a straight line. The line is 10 m long and makes a 30-degree angle with the horizontal. How much work does the gravitational force do on the object?

50 J

The equation for a particular force as a function of position is Fx(x) = (4 N/m)x. How much work does this force do on a particle that moves from x = 0 m to x = 5 m?

50 J

Select all of the following that are forms of energy.

Acoustic Internal Translational kinetic

Rank the following according to the instantaneous power, with the largest instantaneous power at the top and the smallest at the bottom.

Force= (10 N, north), velocity = (10m/s, north) Force= (20 N, north), velocity = (20m/a, east) Force= (30 N, north), Velocity = (30m/s, south)

A book slows down as it slides across a floor that is horizontal, neither tilted up nor down. Select all of the following statements that are true.

Friction converts kinetic energy into internal energy. Both the temperature of the book and the temperature of the floor increase.

A ball is thrown off the top of a building and lands on the ground below. Which quantities are needed to determine the kinetic energy of the ball just before it hits the ground?

Initial gravitational potential energy Initial kinetic energy Final gravitational potential energy

A spring is displaced from equilibrium by some distance x. If it had instead been displaced by a distance of 2x, how would this amount of work done by the spring compare to the actual amount done?

It would be four times larger.

You are holding a heavy box of books for a friend moving into his apartment. You are sweating like mad while your friend searches for his keys to open the door. Are you doing positive, negative, or no work on the box during this process?

No work

Select all of the following units that are equivalent to joules.

N⋅m kg⋅m2/s2

Choose the correct equation for instantaneous power. Theta is the angle between the force and velocity, and the angle between the force and displacement.

P = Fv cosΘ

Select all of the following that could be the work done on a particle initially at rest.

Positive Zero

An ideal rope-and-pulley system is used to lift a pallet of bricks. The advantage of an ideal rope-and-pulley system is that less force is required to lift the object than if it were lifted without mechanical aid. Which statement is correct?

The distance the rope is pulled is greater than it would be if the mechanical aid were not used.

Rank the following in terms of kinetic energy with the largest kinetic energy at the top and the smallest at the bottom.

m= 20 kg, v= 20 m/s m= 10 kg, v= 20 m/s m= 20 kg, v= 10 m/s m= 10 kg, v= 10 m/s

Rank from the smallest at top to the largest at the bottom the work done by a spring resulting from stretching or compressing the spring the specified distance. Assume that the spring constant is constant and that the spring is initially neither stretched nor compressed.

x = -8cm x = 6cm x = -2cm x = 0

Which of the following corresponds to the equation Fx = -kx?

Hooke's law

Rank the work done by the gravitational force with the largest work done at the top and the smallest at the bottom.

lowered 10m 10N is stationary is raised 5m raised 10m

Is kinetic energy a vector or a scalar?

scalar

The force acting on an object and the object's displacement are in opposite directions. Select all of the following that are possible values for the work done on the object.

-20 J

Select all of the following that always occur when work is done.

Energy is transferred. An object moves. A force acts.

Rank the following according to the average power, with the largest average power at the top and the smallest at the bottom.

Energy transferred = 100 J, elapsed time = 10s Energy transferred = 100 J, elapsed time = 20s Energy transferred = 200 J, elapsed time = 50s

A block is held some distance above a vertically oriented, relaxed spring. Which quantities are needed to determine the lowest point the block reaches after it is released?

Final gravitational potential energy Initial elastic potential energy Initial gravitational potential energy Final elastic potential energy

The______ done by a conservative force is independent of the path taken.

work