Motion on Flat Circular Tracks & Friction — IISER Physics MCQs with Solutions
Free IISER Physics Motion on Flat Circular Tracks & Friction MCQs with step-by-step solutions (8 questions). Part of Circular Motion. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Motion on Flat Circular Tracks & Friction · easy · theory
On a flat (unbanked) road, the centripetal force for a turning car is provided by:
A. Static friction between the tyres and the road ✓ Correct
B. The engine thrust directly
C. The normal reaction
D. The car's weight
Solution: Friction is the only horizontal force available on level ground; v_max = √(μrg).
Q2 — Motion on Flat Circular Tracks & Friction · medium · theory
The maximum safe speed on a flat circular road is independent of:
A. The mass of the vehicle ✓ Correct
B. The value of g
C. The radius of the turn
D. The coefficient of friction
Solution: μmg = mv²/r ⇒ v_max = √(μrg) — mass cancels. Trap: heavier cars can NOT corner faster on this account.
Q3 — Motion on Flat Circular Tracks & Friction · easy · numerical
A car turns on a flat road of radius 45 m with μ = 0.5. The maximum safe speed is:
A. 22.5 m/s
B. 15 m/s ✓ Correct
C. 30 m/s
D. 9 m/s
Solution: v = √(μrg) = √(0.5×45×10) = √225 = 15 m/s.
Q4 — Motion on Flat Circular Tracks & Friction · medium · numerical
A coin sits 0.2 m from the centre of a turntable (μ = 0.5). The maximum angular speed before it slips is:
A. 2.5 rad/s
B. 5 rad/s ✓ Correct
C. 10 rad/s
D. 25 rad/s
Solution: μg = ω²r ⇒ ω = √(μg/r) = √(0.5×10/0.2) = √25 = 5 rad/s.
Q5 — Motion on Flat Circular Tracks & Friction · hard · numerical
A car circles a flat track at the maximum safe speed for radius r. To take a turn of radius r/4 on the same surface, its maximum speed must be:
A. Half the original ✓ Correct
B. Unchanged
C. A quarter of the original
D. Twice the original
Solution: v_max ∝ √r ⇒ √(1/4) = 1/2 — tighter turns demand much lower speeds.
Q6 — Motion on Flat Circular Tracks & Friction · medium · numerical
A cyclist at 10 m/s brakes while turning on a flat road of radius 20 m (μ = 0.5, g = 10). The friction needed just for the turn (per kg) is:
A. 2.5 m/s²
B. 10 m/s²
C. 5 m/s² — exactly the friction limit, so no braking margin remains ✓ Correct
D. 1 m/s²
Solution: a_c = v²/r = 100/20 = 5 m/s² = μg — friction is fully used by the turn; any braking causes a skid. This is why you slow BEFORE a corner.
Q7 — Motion on Flat Circular Tracks & Friction · hard · theory
A car takes a level curve while ALSO accelerating forward. Compared with turning at constant speed, the skid threshold speed is:
A. The same
B. Independent of the acceleration
C. Lower, because friction must supply both tangential and centripetal components ✓ Correct
D. Higher
Solution: Friction ≤ μmg must now cover √(F_t² + F_c²); with part of the budget spent on F_t, the centripetal capacity — and hence the safe speed — drops.
Q8 — Motion on Flat Circular Tracks & Friction · hard · numerical
A coin slips on a turntable at 30 rpm when placed 16 cm out. At 60 rpm, the maximum radius at which it can stay is:
A. 1 cm
B. 4 cm ✓ Correct
C. 8 cm
D. 2 cm
Solution: μg = ω²r ⇒ r ∝ 1/ω². Doubling ω divides r by 4: 16/4 = 4 cm.