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Motion In Straight Line

Question
CBSEENPH11026351

A rod PQ of length l is moving with ends remaining in contact with frictionless wall and floor. If at the instant, shown the velocity of end Q is 2 m/s towards negative direction of x. The speed of end P will be

   

  • 3 ms-1

  • 23 ms-1

  • 2 ms-1

  • 52 ms-1

Solution

B.

23 ms-1

From the diagram in question

             x = l cosθ 

             y = l sinθ

∴           vx = dxdt  = -l sinθdt                ..... ddtcosθ =-sinθ 

             vydydt = l cosθ dt

∴            vy vx= - cot θ                         .....cos θsin θ = cot θ

           vy = - vx cot θ

Since      vx = -2 m/s

          vy = -2 cot 60o                ....( Given:- θ = 60o )

               = - 2 × 13

         vy- 23ms-1

The negative sign indicates the motion towards negative direction of Y.