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SocraticPhysics > 5. Work and energy > Flashcards

5. Work and energy Flashcards

1
Q

The work done on an object is directly proportional to what?

A

The force on an object, its displacement, and the cosine of their angle.

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2
Q

What is energy?

A

The ability to do work.

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3
Q

Is work a scalar quanity?

A

Yes.

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4
Q

When is work equal to zero?

A

When the force is perpendicular to an object’s displacement or when it isn’t displaced.

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5
Q

What is kinetic energy?

A

The amount of energy an object has by being in motion.

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6
Q

Kinetic energy, KE, is directly proportional to mass and the square of what?

A

Velocity.

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7
Q

What is the work-energy principle?

A

The net work, W, done on an object is equal to the change in kinetic energy of the object.

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8
Q

Total energy before and after any process is always what?

A

Equal.

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9
Q

What are the two types of potential energy?

A

Gravitational and elastic.

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10
Q

What is potential energy?

A

The energy stored in an object based on its position.

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11
Q

Gravitational potential energy is directly related to what?

A

Mass, acceleration due to gravity, and height above the zero point.

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12
Q

Elastic potential energy is directly proportional to what?

A

Spring constant and displacement of spring from equilibrium squared.

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13
Q

What does the conservation of energy principle say?

A

Energy cannot be created or destroyed, only transferred.

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14
Q

What happens to total mechanical energy in a closed system?

A

It stays the same.

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15
Q

What is the unit of power?

A

Watt.

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16
Q

What is a watt?

A

One joule of work done per second.

17
Q

Power is directly proportional to what?

A

Energy transferred.

18
Q

Total mechanical energy of a pendulum does what?

A

Stays the same.

19
Q

As a pendulum swings back and forth, the total energy stays the same, but it does transfer between what?

A

Gravitational potential energy and kinetic energy.

20
Q

In a pendulum swing, when is gravitational potential energy at its highest, and when is kinetic energy at its highest?

A

Gravitational potential energy is at its highest when it is at the highest point of the swing, and kinetic energy is at its highest at the lowest part of the swing.

21
Q

Which of the following is NOT an example of kinetic energy being converted to potential energy?

  • a basketball player jumping for a rebound
  • releasing a compressed spring
  • squeezing a rubber ball
  • pulling a sled up a hill
A

Releasing a compressed spring

22
Q

Which one is doing the most work?

  • pulling a box 10 m with a force of 100 N
  • pushing a box 100 m with a force of 200N
  • pulling a sled 1000 m with a force of 10N
  • pushing a car with a force of 100000 N and it doesn’t move
A

Pushing a box 100 m with a force of 200N

23
Q

A 100-kg rock is 100 m above the ground, what is the potential energy of the rock?

A

98000 J

24
Q

An example of potential energy is

  • a basketball sitting on a rack.
  • a bird flying.
  • Grandma rocking in her chair.
  • none of the above.
A

A basketball sitting on a rack.

25
Q

A car or truck moving down the highway has what type of energy by virtue of its motion?

A

Kinetic.

26
Q

Ethan carried a 200 Newton bag 3 meters up a ladder in 30 seconds. How much power did he use?

A

20 Watts.

27
Q

Which situation is an example of increasing potential energy?

  • a bicyclist stopping at a stop sign
  • a cat jumping from a tree
  • emptying a bucket of water
  • pulling a wagon uphill
A

Pulling a wagon uphill.

28
Q

An arrow in a bow has 70 J of potential energy. Assuming no loss of energy due to heat, how much kinetic energy will it have after it has been shot?

A

70 J

29
Q

Imagine an object held at some height above the ground. It is released and falls toward the ground. Ignoring air resistance or friction, which of the following must be true?

  • Before it falls, all of its energy must be potential energy.
  • At the end of its fall, all of its energy must be converted to kinetic energy.
  • During its fall, the combination of its kinetic and potential energy must equal the amount of potential energy with which it started.
  • All of the above are true
A

All of the above are true

30
Q

An object with the mass of .1 kg was dropped from a cliff 200 m high. Immediately before hitting the ground, it was clocked to travel with the speed of 40 m/s.

Calculate how much energy was dissipated by the air drag.

A

120 J

SocraticPhysics (18 decks)

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