# The driver of a three wheeler with a speed of 36km/h sees a child in the middle of the road and brings his vehicle to rest in 4s just in time to save the child. What is the average retarding force on the vehicle? The mass of the three-wheeler is 400kg and the mass of the driver is 65kg.

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The driver of a three wheeler with a speed of 36km/h sees a child in the middle of the road and brings his vehicle to rest in 4s just in time to save the child. What is the average retarding force on the vehicle? The mass of the three-wheeler is 400kg and the mass of the driver is 65kg.

(a) 116.25 N

(b) 2122 N

(c) 1162.5 N

(d) 212.2 N

The question was asked in an interview.

The above asked question is from Friction and Forces in portion Laws of Motion of Engineering Physics I

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The correct choice is (c) 1162.5 N

Explanation: u = 36km/h=10m/s, v = 0,

t = 4s, m = 400+65kg = 465kg

v=u+at; a = -2.5m/s^2

Magnitude of the retarding force on the vehicle is

F = ma = 465×2.5 = 1162.5N.

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