A car 2 m wide is parked along the edge of a road. At the instant, the car is started, a boy standing 6 m ahead of the car begins to cross the road with constant speed vs. If the acceleration of the car 1.5 ms-2 and if it continues to move along the edge, then the minimum value of v0=(n)12ms−1 for which boy can avoid collide. The value of n is ____
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answer is 8.
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Detailed Solution
Here, t=dv0sinθ=2v0sinθ and 6+v0tcosθ=12at2⇒ 6+v0tcosθ=1.52t2⇒ 6+v0cosθ2v0sinθ=1.522v0sinθ2⇒ 6+2cotθ=36+2cotθ⇒ v02sin2θ=36+2cotθ⇒ v02=3(6+2cotθ)sin2θFor minimum value of v02,y=(6+2cotθ)sin2θ should be maximum. ∴ dydθ=12sinθcosθ+2cos2θ 6sin2θ+2cos2θ=0 Or tan2θ=−26=−13∴ v0min2=36sin2θ+sin2θPutting the value of θ,v0min2=8⇒v0min=8ms−1∴ n=8