Kinetic & Potential Energy — Drills · Grade 12 Science

Chapter: Work, Energy & Momentum

What these drills covers

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

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

Vocabulary used: kinetic energy, gravitational potential energy, elastic potential energy, spring constant (k), reference level.

Problem 1

Find the kinetic energy of a 3.0 kg ball moving at 4.0 m/s.
Answer and explanation

24 J

KE = ½mv² = ½ × 3.0 × 4.0² = ½ × 3.0 × 16 = 24 J.

Problem 2

Find the gravitational potential energy of a 2.0 kg object 5.0 m above the ground. (g = 9.8 m/s²)
Answer and explanation

98 J

PE = mgh = 2.0 × 9.8 × 5.0 = 98 J.

Problem 3

A spring with spring constant k = 600 N/m is compressed 0.10 m. Find the elastic potential energy stored.
Answer and explanation

3 J

PE = ½kx² = ½ × 600 × 0.10² = ½ × 600 × 0.01 = 3.0 J.

Problem 4

Doubling only the mass of a moving object (keeping its speed the same) changes its kinetic energy by a factor of…
  1. 1 (no change)
  2. ½
  3. 4
  4. 2
Answer and explanation

2

KE = ½mv² is directly proportional to mass, so doubling the mass simply doubles the kinetic energy.

Problem 5

In terms of energy, explain why a dropped object speeds up as it falls.
Answer and explanation

As the object falls, its height decreases, so its gravitational potential energy (PE = mgh) decreases. That energy is converted into kinetic energy (KE = ½mv²), and since kinetic energy grows, the object's speed increases as it drops.

Problem 6

A 5.0 kg object has 160 J of kinetic energy. Find its speed.
Answer and explanation

8 m/s

160 = ½ × 5.0 × v² = 2.5v², so v² = 64 and v = 8.0 m/s.

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