Kinetic & Potential Energy — Drills · Grade 8 Science

Chapter: Energy & Heat Transfer

What these drills covers

By the end of Kinetic & Potential Energy you should be able to:

8 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: energy, kinetic energy, potential energy, joule (J), model, evidence, system boundary, assumption.

Problem 1

Kinetic energy is the energy of
  1. position
  2. motion
  3. temperature
  4. charge
Answer and explanation

motion

Kinetic energy depends on mass and speed.

Problem 2

Lifting a book onto a shelf increases its
  1. kinetic energy
  2. gravitational potential energy
  3. thermal energy
  4. mass
Answer and explanation

gravitational potential energy

Raising an object stores energy by virtue of its position in the gravitational field.

Problem 3

An object's speed doubles. Its kinetic energy becomes how many times larger?
Answer and explanation

4

Kinetic energy depends on the square of the speed, so doubling the speed gives 2² = 4 times the energy.

Problem 4

A 2 kg mass is lifted 5 m where g is 9.8 N/kg. How many joules of gravitational potential energy does it gain?
Answer and explanation

98 J

GPE = mgh = 2 × 9.8 × 5 = 98 J.

Problem 5

How much gravitational potential energy does a 4 kg mass gain when raised 3 m, with g = 9.8 N/kg?
Answer and explanation

117.6 J

4 × 9.8 × 3 = 117.6 J.

Problem 6

At the highest point of its flight, a thrown ball has
  1. maximum kinetic energy
  2. maximum gravitational potential energy
  3. no energy
  4. maximum mass
Answer and explanation

maximum gravitational potential energy

It is highest and slowest there, so potential energy is greatest and kinetic least.

Problem 7

Explain why doubling an object's mass doubles its kinetic energy but doubling its speed quadruples it.
Answer and explanation

Kinetic energy depends on mass to the first power and on speed squared. Doubling mass multiplies the energy by two, while doubling speed multiplies it by two twice over, giving four times. This is why a small increase in speed matters so much more than the same proportional increase in mass — and why stopping distances grow sharply with speed.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Describe the energy changes as a swing moves from its highest point to its lowest and back.
Answer and explanation

At the highest point the swing is momentarily still, so its energy is almost entirely gravitational potential. As it falls, that store converts to kinetic energy, which is greatest at the lowest point where the swing moves fastest. Rising on the other side reverses the conversion. Each swing is slightly lower than the last because some energy transfers to the surroundings through air resistance and friction at the pivot.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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