Physics Q28 – JEE-MAIN 2026

Home Physics Motion in a PlaneQuestion #305

A car moving with a speed of

54 km/h

takes a turn of radius

20 m

. A simple pendulum is suspended from the ceiling of the car. Determine the angle made by the string of the pendulum with the vertical during the turning. (Take

g = 10 {m/s}^{2}

)

Clue 1 of 3: Frame of Reference

Consider the forces acting on the pendulum bob in the non-inertial frame of the car.

🧠 Full Solution Path

Step 1: Convert speed and identify forces✦ Active

Convert the car's speed from $km/h$ to $m/s$ . In the non-inertial frame of the car, the pendulum bob experiences gravitational force vertically downwards and a pseudo-force (due to centripetal acceleration) horizontally outwards.

v = 54 km/h = 54 \times \frac{5}{18} m/s = 15 m/s

Step 2: Calculate horizontal acceleration○ Expand

Determine the horizontal acceleration (centripetal acceleration) experienced by the car and thus by the pendulum bob.

a_{h} = \frac{v^{2}}{R} = \frac{(15 m/s)^{2}}{20 m} = \frac{225}{20} {m/s}^{2} = 11.25 {m/s}^{2}

Step 3: Determine the angle○ Expand

The angle $θ$ made by the pendulum string with the vertical is given by the ratio of the horizontal acceleration to the acceleration due to gravity.

\tan θ = \frac{a_{h}}{g} = \frac{11.25}{10} = 1.125

θ = \tan^{- 1} (1.125)

💡 Teacher's Secret Hint

Ensure units are consistent before calculation.

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Physics Question 28 – JEE-MAIN 2026

Clue 1 of 3: Frame of Reference

🧠 Full Solution Path