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The driver of a three-wheeler moving with a speed of 36 km/h sees a child standing in the middle of the road and brings his vehicle to rest in 4.0 s just in time to save the child. What is the average retarding force on the vehicle? The mass of the three-wheeler is 400 kg and the mass of the driver is 65 kg. |
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Answer» Initial speed of the three-wheeler, u = 36 km/h Final speed of the three-wheeler, v = 10 m/s Time, t = 4 s Mass of the three-wheeler, m = 400 kg Mass of the driver, m' = 65 kg Total mass of the system, M = 400 + 65 = 465 kg Using the first law of motion, the acceleration (a) of the three-wheeler can be calculated as: v = u + at a = (v - u)/t = (0 - 10)/4 = -2.5 m/s2 The negative sign indicates that the velocity of the three-wheeler is decreasing with time. Using Newton’s second law of motion, the net force acting on the three-wheeler can be calculated as: F = Ma = 465 × (–2.5) = –1162.5 N The negative sign indicates that the force is acting against the direction of motion of the three-wheeler |
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