Projectile & Two-Dimensional Motion — Drills · Grade 12 Science

Chapter: Motion & Kinematics

What these drills covers

By the end of Projectile & Two-Dimensional Motion you should be able to:

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

Vocabulary used: projectile, trajectory, horizontal component, vertical component, range, independence of motion.

Problem 1

A ball leaves a table horizontally at 8 m/s and is in the air for 0.5 s. How far from the base of the table does it land?
Answer and explanation

4 m

Horizontal motion is constant velocity: x = (8)(0.5) = 4 m.

Problem 2

During a projectile's flight (ignoring air resistance), its vertical acceleration is…
  1. 9.8 m/s² downward
  2. increasing with speed
  3. zero
  4. dependent on its horizontal velocity
Answer and explanation

9.8 m/s² downward

The vertical motion is free fall, so the acceleration is a constant 9.8 m/s² downward the entire flight.

Problem 3

A stone is thrown horizontally from a 19.6 m high wall. How long until it hits the ground? (g = 9.8 m/s²)
Answer and explanation

2 s

Vertical motion: 19.6 = ½(9.8)t² = 4.9t², so t² = 4.0 and t = 2.0 s.

Problem 4

A ball is thrown horizontally at 25 m/s from a 44.1 m high cliff. How far from the base does it land? (g = 9.8 m/s²)
Answer and explanation

75 m

Time to fall: 44.1 = 4.9t², so t² = 9.0 and t = 3.0 s. Range = (25)(3.0) = 75 m.

Problem 5

One ball is dropped and, at the same instant from the same height, an identical ball is thrown horizontally. Which lands first?
  1. the thrown ball lands first
  2. the dropped ball lands first
  3. both land at the same time
  4. it depends on the throwing speed
Answer and explanation

both land at the same time

Vertical and horizontal motions are independent, so both balls are in identical free fall and land at the same time.

Problem 6

Explain what is meant by the 'independence' of a projectile's horizontal and vertical motions.
Answer and explanation

It means the horizontal motion and the vertical motion happen separately and don't affect each other's timing. Gravity only changes the vertical motion, pulling the object down at g, while the horizontal velocity stays constant because no horizontal force acts. The two motions share only the time in the air, so you can solve each as its own one-dimensional problem — the horizontal speed has no effect on how long the object takes to fall.

Browse all courses