Motion and Newton's laws

Written by Dr. Hamza Farooq (Physics)

MDCAT · Physics · 8 questions

Name: ____________________ Date: ____________

A car starts from rest and reaches 20 m/s in 5 s with uniform acceleration. What is its acceleration?
- A 4 m/s²
- B 100 m/s²
- C 5 m/s²
- D 2 m/s²
A car starts from rest and reaches 20 m/s in 5 s with uniform acceleration. How far does it travel in those 5 s?
- A 20 m
- B 100 m
- C 50 m
- D 25 m
What force gives a 2 kg mass an acceleration of 3 m/s²?
- A 9 N
- B 6 N
- C 5 N
- D 1.5 N
The SI unit of momentum is:
- A kg m²/s
- B kg m/s
- C N s²
- D kg m/s²
For a projectile fired from level ground, the range is greatest when the angle of projection is:
- A 30 degrees
- B 60 degrees
- C 45 degrees
- D 90 degrees
A stone is dropped from rest. Taking g = 10 m/s² and ignoring air resistance, what is its speed after 3 s?
- A 15 m/s
- B 45 m/s
- C 10 m/s
- D 30 m/s
A 1000 kg car moving at 10 m/s is brought to rest in 5 s. What is the average braking force?
- A 500 N
- B 2000 N
- C 10000 N
- D 1000 N
Newton's third law says that when body A exerts a force on body B:
- A B exerts no force on A
- B B exerts an equal and opposite force on A
- C B exerts a force on A in the same direction
- D B exerts a smaller force on A

Answer key

1. A, 2. C, 3. B, 4. B, 5. C, 6. D, 7. B, 8. B

a = (v - u) / t = (20 - 0) / 5 = 4 m/s².
s = (u + v) / 2 x t = (0 + 20) / 2 x 5 = 50 m.
F = ma = 2 x 3 = 6 N.
Momentum is mass times velocity, so its unit is kg m/s, which is the same as N s.
Range depends on sin 2θ, which is largest when 2θ = 90 degrees, so θ = 45 degrees (ignoring air resistance).
v = u + gt = 0 + 10 x 3 = 30 m/s.
Force = change in momentum / time = (1000 x 10) / 5 = 2000 N.
Forces come in action-reaction pairs. They are equal in size, opposite in direction and act on different bodies.