Lesson test: Work and kinetic energy

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Work and kinetic energy

1.[2p]
A 1200 kg car travels at 25 m s⁻¹. What is its kinetic energy, in kilojoules?

CorrectNot quite: 375

2.[2p]
Why does the normal force do no work on a block sliding along a horizontal floor?

It is perpendicular to the displacement, so the cosine in $F s \cos φ$ is zero

Correct

It is smaller than the weight

The answer is: It is perpendicular to the displacement, so the cosine in $Fs\cos\phi$ is zero

It is cancelled by the weight

The answer is: It is perpendicular to the displacement, so the cosine in $Fs\cos\phi$ is zero

It acts at a point that is instantaneously at rest

The answer is: It is perpendicular to the displacement, so the cosine in $Fs\cos\phi$ is zero

3.[2p]
A rope pulls a crate 8.0 m along the floor with a force of 60 N at 40° above the horizontal. How much work does the rope do, in joules?

CorrectNot quite: 368

4.[2p]
A spring of stiffness 400 N m⁻¹ is compressed 0.25 m. How much work is stored in it, in joules?

CorrectNot quite: 12.5

5.[2p]
Doubling the speed of a car doubles the distance needed to stop it under the same braking force.

True

The answer is: False

False

Correct

6.[2p]
A cyclist and machine of total mass 80 kg climb a slope at 4.0 m s⁻¹, needing 240 W against gravity alone. What gravitational force component are they working against, in newtons?

CorrectNot quite: 60

7.[3p]
Which of these forces do zero work in the situations described?

Select all that apply

The tension in the string of a conical pendulum, on the bob

Correct

Gravity on a satellite in a perfectly circular orbit

Correct

The normal force on a block sliding down an incline

Correct

Kinetic friction on a block sliding along a floor

The answer is: The tension in the string of a conical pendulum, on the bob, Gravity on a satellite in a perfectly circular orbit, The normal force on a block sliding down an incline

8.[3p]
A 0.60 kg block is launched by a spring of stiffness 900 N m⁻¹ compressed by 0.20 m, on a frictionless surface. What speed does it leave at, in metres per second?

CorrectNot quite: 7.75

9.[2p]
Match each quantity to its SI unit.

Work
Power
Spring stiffness
Kinetic energy

watt
joule
joule
newton per metre

Show the answer

Work: joule Power: watt Spring stiffness: newton per metre Kinetic energy: joule

1.[2p] A 1200 kg car travels at 25 m s⁻¹. What is its kinetic energy, in kilojoules?

2.[2p] Why does the normal force do no work on a block sliding along a horizontal floor?

3.[2p] A rope pulls a crate 8.0 m along the floor with a force of 60 N at 40° above the horizontal. How much work does the rope do, in joules?

4.[2p] A spring of stiffness 400 N m⁻¹ is compressed 0.25 m. How much work is stored in it, in joules?

5.[2p] Doubling the speed of a car doubles the distance needed to stop it under the same braking force.

6.[2p] A cyclist and machine of total mass 80 kg climb a slope at 4.0 m s⁻¹, needing 240 W against gravity alone. What gravitational force component are they working against, in newtons?

7.[3p] Which of these forces do zero work in the situations described?

8.[3p] A 0.60 kg block is launched by a spring of stiffness 900 N m⁻¹ compressed by 0.20 m, on a frictionless surface. What speed does it leave at, in metres per second?

9.[2p] Match each quantity to its SI unit.

1.[2p]
A 1200 kg car travels at 25 m s⁻¹. What is its kinetic energy, in kilojoules?

2.[2p]
Why does the normal force do no work on a block sliding along a horizontal floor?

3.[2p]
A rope pulls a crate 8.0 m along the floor with a force of 60 N at 40° above the horizontal. How much work does the rope do, in joules?

4.[2p]
A spring of stiffness 400 N m⁻¹ is compressed 0.25 m. How much work is stored in it, in joules?

5.[2p]
Doubling the speed of a car doubles the distance needed to stop it under the same braking force.

6.[2p]
A cyclist and machine of total mass 80 kg climb a slope at 4.0 m s⁻¹, needing 240 W against gravity alone. What gravitational force component are they working against, in newtons?

7.[3p]
Which of these forces do zero work in the situations described?

8.[3p]
A 0.60 kg block is launched by a spring of stiffness 900 N m⁻¹ compressed by 0.20 m, on a frictionless surface. What speed does it leave at, in metres per second?

9.[2p]
Match each quantity to its SI unit.