Kinematics 5 Question 12

13. An object A is kept fixed at the point x=3m and y=1.25m on a plank P raised above the ground. At time t=0, the plank starts moving along the +x-direction with an acceleration 1.5m/s2. At

the same instant, a stone is projected from the origin with a velocity u as shown. A stationary person on the ground observes the stone hitting the object during its downward motion at an angle of 45 to the horizontal. All the motions are in xy plane. Find u and the time after which the stone hits the object. (Take g=10m/s2 ).

(2000, 10M)

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Answer:

Correct Answer: 13. u=(3.75i^+6.25j^)m/s,1s

Solution:

  1. Let t be the time after which the stone hits the object and θ be the angle which the velocity vector u makes with horizontal. According to question, we have following three conditions.

Vertical displacement of stone is 1.25m.

$$



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