Friction — Homi Bhabha Class 9 Physics MCQs with Solutions
Free Homi Bhabha Class 9 Physics Friction MCQs with step-by-step solutions (10 questions). Part of Laws of Motion & Force. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Friction · medium · theory
The force of friction between two surfaces always acts:
A. opposite to the direction of relative motion ✓ Correct
B. downward
C. in the direction of motion
D. perpendicular to the surface
Solution: Friction opposes (or tends to oppose) the relative motion between the surfaces in contact.
Q2 — Friction · medium · theory
Ball bearings are used in machines because:
A. rolling friction is larger than sliding friction
B. they eliminate friction completely
C. rolling friction is much smaller than sliding friction ✓ Correct
D. they increase friction
Solution: Converting sliding into rolling greatly reduces friction, since rolling friction is much smaller.
Q3 — Friction · hard · theory
For two given surfaces, which statement is correct?
A. Friction is zero once motion starts
B. Kinetic friction is greater than static friction
C. Limiting (maximum static) friction is greater than kinetic friction ✓ Correct
D. Both are always equal
Solution: It takes a larger force to start motion than to keep it going, so limiting static friction exceeds kinetic friction.
Q4 — Friction · hard · numerical
A block presses on a surface with a normal force of 50 N. If the coefficient of friction is 0.2, the frictional force is:
A. 50.2 N
B. 10 N ✓ Correct
C. 250 N
D. 2.5 N
Solution: Friction $= \mu N = 0.2 \times 50 = 10$ N.
Q5 — Friction · medium · theory
The treads (grooves) on vehicle tyres are provided to:
A. increase friction (grip) with the road ✓ Correct
B. reduce friction with the road
C. make the tyre look attractive
D. reduce the weight of the tyre
Solution: Treads increase the grip (friction) between tyre and road, improving traction and braking.
Q6 — Friction · hard · theory
Assertion (A): Friction is called a "necessary evil". Reason (R): Friction wastes energy as heat but is also needed for walking and braking.
A. Both A and R are true but R is NOT the correct explanation of A
B. Both A and R are true and R is the correct explanation of A ✓ Correct
C. A is false but R is true
D. A is true but R is false
Solution: Friction both wastes energy (evil) and is essential for walking/gripping (necessary) — R correctly explains why it is a necessary evil.
Q7 — Friction · easy · theory
The force of friction between two surfaces in contact always acts:
A. vertically downward
B. opposite to the direction of relative motion ✓ Correct
C. in the direction of motion
D. perpendicular to the surfaces
Solution: Friction is a resistive force; it always opposes the relative motion (or tendency of motion) between the surfaces in contact.
Q8 — Friction · easy · theory
Which of the following is the best way to reduce friction between two moving machine parts?
A. pressing the surfaces harder together
B. making the surfaces rougher
C. increasing the load on the parts
D. applying a lubricant such as oil ✓ Correct
Solution: A lubricant forms a thin layer that separates the surfaces and fills the tiny grooves, greatly reducing friction; the other options all increase friction.
Q9 — Friction · medium · theory
For the same pair of surfaces and the same load, which type of friction is usually the smallest?
A. limiting friction
B. sliding friction
C. static friction
D. rolling friction ✓ Correct
Solution: For a given pair of surfaces, rolling friction is smaller than sliding friction, which is smaller than the maximum static (limiting) friction; hence rolling is the smallest.
Q10 — Friction · hard · theory
Ball bearings are fitted between the moving parts of many machines mainly to:
A. increase the friction so the parts grip better
B. replace sliding friction with the much smaller rolling friction ✓ Correct
C. remove friction completely from the machine
D. increase the area of contact between the parts
Solution: The balls roll instead of slide, converting sliding friction into rolling friction, which is far smaller; this reduces wear and energy loss. Friction can be reduced but never made exactly zero.