AS-LEVEL: Projectile Motion (PMT AQA pre-2016)

Question 1

what does “assume there is no air resistance” mean in terms of horizontal motion?

Answer 1

-since there’s no air resistance, no horizontal forces act on the object

• horizontal acceleration = 0ms-2
• ∴ horizontal velocity stays constant
• ∴ we use v=s/t

Question 2

what does “assume there is no air resistance” mean in terms of vertical motion?

Answer 2

-‘no air resistance’ means the only vertical force is weight (due to g)

• ∴ constant vertical acceleration = 9.81ms-2
• ∴ must use suvat

(CANNOT use v=s/t)

Question 3

Rifle B is fired and the bullet emerges with a smaller horizontal velocity than the bullet from rifle A.
Explain why the horizontal distance travelled by bullet B will be less than bullet A.

(3 marks)

Answer 3

-both have same vertical acceleration (due to gravity)

• ∴ same time of flight (t is constant for A & B)
• ∴ s horizontal is proportional to v horizontal
• v horizontal A > v horizontal B
• ∴ s horizontal A > s horizontal B