Level: JHS, Basic 9 | Subject: Integrated Science | Strand: Forces and Energy | Topic: Newton’s Laws of Motion and Momentum
Read the summary notes first: Basic 9 Integrated Science Summary Notes: Newton’s Laws of Motion and Momentum
Test Yourself: 20 Objective Questions
Tick one answer for each question, then press Review answer. If your answer is wrong, it will be marked first, then the correct answer will show in green.
Essay Questions
- State Newton’s three laws of motion and give one everyday example of each. (6 marks)
- A force of 90 N acts on a box of mass 15 kg on a smooth floor. (a) Calculate the acceleration of the box. (b) Calculate its speed after 4 seconds, starting from rest. (5 marks)
- Define momentum. Calculate the momentum of a car of mass 800 kg moving at 15 m/s. (4 marks)
- A trolley of mass 2 kg moving at 6 m/s collides with a stationary trolley of mass 4 kg and the two stick together. Calculate their common speed after the collision. State the principle you used. (5 marks)
- Use Newton’s third law to explain how (a) a swimmer moves forward and (b) a gun recoils when fired. (4 marks)
Essay Questions: Marking Guide for Teachers and Parents
- (6 marks) First law: an object stays at rest or moves at constant speed in a straight line unless a resultant force acts on it (1). Example: passengers lean forward when a trotro brakes suddenly (1). Second law: force equals mass times acceleration, F = ma (1). Example: a heavier car needs a bigger force for the same acceleration (1). Third law: for every action there is an equal and opposite reaction (1). Example: walking, a rocket, or a swimmer pushing the water backward (1).
- (5 marks) (a) a = F / m (1) = 90 / 15 (1) = 6 m/s2 (1). (b) v = a x t = 6 x 4 (1) = 24 m/s (1).
- (4 marks) Momentum is the quantity of motion of an object and equals mass multiplied by velocity (1). p = m x v (1) = 800 x 15 (1) = 12 000 kg m/s with the correct unit (1).
- (5 marks) Momentum before = 2 x 6 = 12 kg m/s (1). Momentum after = (2 + 4) x v = 6v (1). 6v = 12 (1), so v = 2 m/s (1). Principle: conservation of momentum, because total momentum before equals total momentum after when no outside force acts (1).
- (4 marks) (a) The swimmer pushes the water backward (1), and the water pushes the swimmer forward with an equal force (1). (b) The gun pushes the bullet forward (1), and the bullet pushes the gun backward, which is the recoil (1).
Education Always (education.inspiringalways.com). Original practice questions, not official WAEC or BECE questions.