Question

A boy (30 kg) sitting on his horse whips it. The horse speeds up at an average acceleration of 2.0 m/s 2.If the boy slides back during the acceleration, what can be said about the coefficient of static friction between the horse and the boy.

(a) 0.10

(b) 0.20

(c) 0.30

(d) 0.40

This question was posed to me in a dream while sleeping

Question is from Laws of Solid Friction and Limiting Friction topic in chapter Friction of Machine Kinematics

Answer 1

Right option is (b) 0.20

For explanation: If the boy slides back, the horse could not exert a

friction of 60 N on the boy. The maximum force of static

friction that the horse may exert on the boy is

fs = μs = μsMg

μs(30 kg) (10m/s^2) = μs 300 N

where μs is the coefficient of static friction. Thus,

μs(300 N) <60 N

or, μs <60/300 = 0.20.