Questions
1. Calculate: A car speeds up from u = 10 m s⁻¹ at a = 2 m s⁻² for t = 5 s. Find the unknown using v = u + at.
v = u + at = 10 + (2 × 5) = 20 m s⁻¹.
2. Calculate: An object starts at u = 4 m s⁻¹ and accelerates at a = 2 m s⁻² for t = 3 s. Find the unknown using s = ut + ½at².
s = ut + ½at² = (4 × 3) + (½ × 2 × 3²) = 12 + 9 = 21 m.
3. Calculate: A trolley starts from rest (u = 0) and accelerates at a = 2 m s⁻² over s = 25 m. Find the unknown using v² = u² + 2as.
v² = u² + 2as = 0 + (2 × 2 × 25) = 100, so v = 10 m s⁻¹.
4. Calculate: A cyclist changes speed from u = 10 m s⁻¹ to v = 30 m s⁻¹ in t = 4 s. Find the unknown using a = (v − u) / t.
a = (v − u) / t = (30 − 10) / 4 = 5 m s⁻².
5. Calculate: Find the momentum of a m = 2 kg ball moving at v = 5 m s⁻¹. Find the unknown using p = mv.
p = mv = 2 × 5 = 10 kg m s⁻¹.
6. Calculate: A resultant force acts on a m = 3 kg block giving a = 2 m s⁻². Find the unknown using F = ma.
F = ma = 3 × 2 = 6 N.
7. Calculate: A m = 0.5 kg ball is kicked from rest (u = 0) to v = 20 m s⁻¹. Find the unknown using Impulse = Ft = mv − mu.
Impulse = mv − mu = (0.5 × 20) − (0.5 × 0) = 10 N s.
8. Calculate: A m = 0.5 kg ball goes from u = 0 to v = 20 m s⁻¹ in a contact time t = 0.02 s. Find the unknown using F = (mv − mu) / t.
F = (mv − mu) / t = (10 − 0) / 0.02 = 500 N.
9. Calculate: Find the weight of a m = 2 kg object where g = 9.81 m s⁻². Find the unknown using W = mg.
W = mg = 2 × 9.81 = 19.62 N ≈ 19.6 N.
10. State the manipulated, responding and constant variables for: To determine the value of gravitational acceleration g by timing a steel ball falling freely through measured heights.
Manipulated: Height of fall, h. Responding: Time of fall, t. Constant: The same steel ball and release mechanism.
11. State the manipulated, responding and constant variables for: To investigate how the inertia of an object, shown by its period of oscillation on an inertial balance, depends on its mass.
Manipulated: Mass loaded on the inertial balance, m. Responding: Period of horizontal oscillation, T. Constant: The inertial balance (its stiffness) and the amplitude of oscillation.
12. Explain: what inertia really is.
Inertia is an object's natural resistance to any change in its state of motion. It depends only on mass, so heavier objects are harder to start and to stop.
13. Explain: why a seatbelt works.
In a crash a seatbelt makes you stop over a longer time. The same change in momentum spread over more time means a smaller, safer force on your body.
14. Explain: why heavier objects do not fall faster.
In free fall every object gains speed at the same rate, because a heavier object also has more inertia to move. Air resistance, not weight, is what usually makes some things fall slower.
15. Define mass.
The amount of matter in an object; a scalar quantity measured in kilograms (kg), and a measure of its inertia.
16. Define momentum.
The product of the mass and velocity of an object; a vector quantity (momentum = mass × velocity), measured in kg m s⁻¹.
17. Define principle of conservation of momentum.
The principle that the total momentum of a system remains constant in the absence of an external force, so total momentum before a collision equals total momentum after.
18. Define force.
A push or pull acting on an object that can change its shape, or its state of rest or motion; a vector quantity measured in newtons (N).
19. Define impulse.
The product of a force and the time for which it acts, equal to the change in momentum it produces; measured in newton seconds (N s).
20. Define impulsive force.
The large force acting over a very short time during a collision or explosion (impulsive force = change in momentum ÷ time).
Marking yourself
- Calculation: formula written, values substituted with units, final answer with unit and sensible significant figures.
- Variables: manipulated = what you change; responding = what you measure; constant = what you keep the same.
- Definition: one sentence, correct physical quantity, correct unit.
Exam tip
More Force and Motion I resources
- Chapter overview: Force and Motion I
- Revision Notes
- Common Mistakes
- Paper 2 Answering Guide
- Paper 3 Guide
- Key Terms
- Calculation practice sets
Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)