A motorcar of mass 1200kg is moving along a straight line with a uniform velocity of 90 km//h. Its velocity is slowed down to 18 km//h in 4s b

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A motorcar of mass 1200kg is moving along a straight line with a uniform velocity of 90 km//h. Its velocity is slowed down to 18 km//h in 4s by an unbalanced external force. Calculate the acceleration and change in momentum. Also, calculate the magnitude of the force required.

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Here, m=1200kg, u=90km//h=(90xx1000m)/(60xx60)=25m//s
v=18km//h=(18xx1000m)/(60xx60s)=5m//s, t=4s
Acceleration, a=(v-u)/t=(5-25)/4= -5m//s^(2)
change in momentum = m(v-u)=1200(5-25)= -24000kg m//s
Change in momentum = m(v-u)=1200(5-25)= -24000kg m//s
Force required, F=ma=1200(-5)= -6000N
Magnitude of force required =6000N
Negative sign shows that force is opposing the motion.