Dynamics

Class 9 · Physics · 6 questions

Name: ____________________ Date: ____________

Newton's first law of motion is also called the law of:
- A Gravitation
- B Acceleration
- C Momentum transfer
- D Inertia
What force is needed to give a mass of 5 kg an acceleration of 3 m/s2?
- A 8 N
- B 1.7 N
- C 15 N
- D 2 N
What is the SI unit of momentum?
- A kg m/s2
- B N
- C J
- D kg m/s
When a gun fires a bullet, the gun recoils. This is explained by:
- A Newton's second law
- B Newton's first law
- C Newton's third law
- D Law of gravitation
What is the weight of a 10 kg mass on Earth? (g = 10 m/s2)
- A 10 N
- B 1 N
- C 100 N
- D 0.1 N
The force that opposes the motion of one surface over another is called:
- A Thrust
- B Friction
- C Tension
- D Gravity

Answer key

1. D, 2. C, 3. D, 4. C, 5. C, 6. B

A body stays at rest or in uniform motion unless a net force acts on it. This property is inertia.
F = m a = 5 x 3 = 15 N.
Momentum = mass x velocity, so its unit is kg m/s.
The force on the bullet has an equal and opposite reaction force on the gun.
W = m g = 10 x 10 = 100 N.
Friction acts between surfaces in contact and opposes relative motion.