5. You wish to measure how tightly an ant can hold on to its substrate. You place an
ant of mass 10 mg on a round, rotating platform at a distance of 30 cm from the
centre, and begin increasing the angular velocity of the rotating platform until the ant
is dislodged. You find that the maximum angular velocity at which the ant can hold
on is 20 rad/s. The maximum force that the ant can exert to hold on is:
a. 0.2 mN
b. 1.2 mN
c. 0.2 N
d. 1.2 N

Ant Centripetal Force on Rotating Platform: Physics MCQ Solution

The maximum force an ant can exert equals the centripetal force required at the point of dislodgement. For an ant of mass 10 mg (0.01 kg) at radius 30 cm (0.3 m) and angular velocity 20 rad/s, this force is F = mrω² = 0.01 × 0.3 × 400 = 1.2 N.

Problem Breakdown

The ant undergoes uniform circular motion until slipping occurs. Centripetal force Fc = mrω² provides the inward acceleration ac = rω², where tangential velocity v = rω. Substituting values yields exactly 1.2 N, matching option d.

Option Analysis

• a. 0.2 mN: Equals 0.0002 N, 6000 times too small—ignores ω² magnitude or confuses milli-newton scale.
• b. 1.2 mN: Equals 0.0012 N, 1000 times too small—likely mistakes mass as 10 μg or omits kg conversion.
• c. 0.2 N: Underestimates by factor of 6; possibly uses ω=10 rad/s or linear velocity directly without squaring.
• d. 1.2 N: Correct, as calculated precisely from standard formula.

The ant maximum force rotating platform experiment measures grip strength through centripetal force at slip point. In this CSIR NET-style physics question, a 10 mg ant at 30 cm radius holds until 20 rad/s, revealing its adhesion limit.

Centripetal Force Formula Derivation

Centripetal acceleration ac = v²/r = rω² leads to Fc = mrω². Here, m=0.01 kg, r=0.3 m, ω=20 rad/s gives Fc=1.2 N—the ant’s maximum tangential grip force.

Biological Physics Application

Ants exhibit remarkable adhesion via setae and van der Waals forces, quantified here at 120 times body weight (1.2 N / 0.0001 N weight). Similar setups test insect biomechanics.