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A motorcar of mass 1200 kg is moving along a straight line with auniform velocity of 90km/h. its velocity isslowed down to 18 km/h in 4 seconds by an unbalanced external force. Calculate the acceleration and change in momentum . Also calculate the magnitude of the force required. |
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Answer» SOLUTION :MASS of the motorcar ,m=1200 kg Initial velocity of the motorcar v=18km/h=5 m/s Time taken ,t=4s According to the first equation of MOTION. v=u+at 5=25+a(4) `a=-5 m//s^2` Negative sign indicate that it.s a retarding motion, i.e velocity is decreasing. Change in momentum =mv-mu=m(v-u) =1200 (5-25)=-2400 kgm/s `F=ma=1200 xx5 =-6000 N `. Acceleration of the motor car `=-5 m//s^2` Change in momentum of the motor car `=-24000 kg m^(-1)` Hence, the force REQUIRED to decrease the velocity is 6000 N . (Negative sign indicate retardation, decrease in momentum and retarding force) |
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