Question

motor car of mass 1200 kg is moving along a straight line with uniform velocity of 90 km per hour its velocity is slowed to 18 kilometre per hour in 4 seconds by an unbalanced external force calculate the acceleration and change in momentum also calculate the magnitude of force required​

Answer 1

SOLUTION :

mass of the motor car, m =1200kg

initial velocity of motor car, u =90km/h=25m/s

final velocity of motor car, v= 18km/h =5m/s

Time taken, t = 4s

according to the first equation of motion: v = u +at

5=25 +a (4)

a= -5m/s²

negative sign indicates that it's a retarding motion i.e velocity is decreasing

change in momentum= mv - mu =m(v-u)

=1200 (5-25) = - 24000 kg ms -¹

force= mass × acceleration = 1200 × -5 = -6000 N

acceleration of the motor car = -5 m/s²

change inh momentum of motor car = -24000 kg m s-¹

Hence, the force required to decrease the velocity is 6000 N (negative sign indicates retardation, decrease in momentum and retardation force................

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