Free Practice Quiz Question List

7 - Power and Energy Applications Online Quiz Questions

Use this free practice quiz with 20 questions to review 7 - Power and Energy Applications, test your knowledge, and prepare for your next test or exam.

20 questions

True or false

1 point

True or false: A watt is a unit of energy rather than a unit of the rate at which energy is transferred.

A
True
B
False

Choose one

1 point

A force acts on an object moving at constant velocity. In which situation does the force deliver zero instantaneous power?

A
The force is parallel to the velocity.
B
The force is opposite the velocity.
C
The force is perpendicular to the velocity.
D
The force has twice the magnitude of the velocity.

Fill in the blank

1 point

Complete the relation for average power: $P_{\text{avg}}=\frac{\Delta E}{\text{$ $}}$ . The denominator is the elapsed quantity.

Written response

1 point

A car travels at constant speed $16\ \text{m/s}$ while a resistive force of $450\ \text{N}$ acts opposite its motion. What mechanical power must the engine supply? Enter the value in kilowatts.

Choose all

1 point

Select all statements that are correct about a power-versus-time graph and the energy transferred.

A
The area under a power-versus-time graph represents transferred energy.
B
The slope of a power-versus-time graph directly represents transferred energy.
C
For constant power, transferred energy equals power multiplied by time.
D
The average power over an interval must equal the greatest power during that interval.
E
A watt-second is equivalent to a joule.

Choose one

1 point

A machine delivers $600\ \text{W}$ of useful output power while receiving $800\ \text{W}$ of input power. What is its efficiency?

A
60%
B
75%
C
80%
D
133%

Fill in the blank

1 point

When friction causes a system's mechanical energy to decrease, the energy is transferred primarily into .

Written response

1 point

What quantity is represented by $W_{\text{ext}}$ in the mechanical energy-accounting equation?

True or false

1 point

True or false: If an object moves at constant speed, no force can be transferring energy to it.

A
True
B
False

Choose all

1 point

Select all statements that correctly describe energy systems and energy accounting.

A
For an isolated system, external work is zero.
B
Changing the zero level of gravitational potential energy does not change predictions based on potential-energy differences.
C
Friction destroys energy from the universe.
D
Constant speed guarantees that every force does zero power.
E
An object-Earth system can include gravitational potential energy.

Choose one

1 point

A crane lifts a $180\ \text{kg}$ load vertically through $10\ \text{m}$ in $6.0\ \text{s}$ at constant speed. What useful mechanical power is delivered to the load? Use $g=9.8\ \text{m/s}^2$ .

A
1.47 kW
B
2.45 kW
C
2.94 kW
D
17.6 kW

Open ended

1 point

A $1.5\ \text{kg}$ block starts from rest at the top of a ramp $4.0\ \text{m}$ above the bottom. Friction transfers $10\ \text{J}$ into thermal energy. Using an appropriate system and energy-accounting equation, determine the block's speed at the bottom and explain how the friction term enters the calculation.

Choose one

1 point

A force of magnitude $50\ \text{N}$ acts at an angle of $60^\circ$ to an object's velocity of $4.0\ \text{m/s}$ . What instantaneous power does the force deliver?

A
0 W
B
100 W
C
200 W
D
346 W

Written response

1 point

A spring has force constant $k=200\ \text{N/m}$ and is compressed by $0.30\ \text{m}$ . What elastic potential energy is stored in the spring? Enter the value in joules.

Choose one

1 point

A device operates at a constant power of $450\ \text{W}$ for $8.0\ \text{s}$ . How much energy does it transfer?

A
450 J
B
3600 J
C
56.25 J
D
360 J

True or false

1 point

True or false: A car traveling at constant speed on a level road can have an engine supplying positive power even though the net work on the car is zero.

A
True
B
False

Choose one

1 point

A force of $80\ \text{N}$ acts on an object moving at $5.0\ \text{m/s}$ . The angle between the force and the velocity is $60^\circ$ . What instantaneous power does the force deliver?

A
0 W
B
400 W
C
200 W
D
80 W

Written response

1 point

A machine produces $1.8\ \text{kW}$ of useful output power while receiving $2.4\ \text{kW}$ of input power. What is its efficiency, expressed as a percentage?

Choose one

1 point

Which statement correctly describes the choice of the zero level for gravitational potential energy?

A
The zero level must always be at ground level.
B
The zero level must be at the object’s initial position.
C
The zero level may be chosen arbitrarily without changing predicted motion.
D
The zero level must be at the object’s final position.

Choose one

1 point

A spring with spring constant $200\ \text{N/m}$ is compressed by $0.15\ \text{m}$ . What elastic potential energy is stored in the spring?

A
2.25 J
B
15 J
C
30 J
D
4.50 J