Question

An object A is kept fixed at the point x = 3 m and y = 1.25 m on a plank Praised above the ground.At time t = 0 the plank starts moving along the + x direction with an acceleration 1.5 m/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 45º to the horizontal.

All the motions are in x – y plane. Find u and the time after which the stone hits the object. Take g = 10 m/s² .

Answer 1

If the stone hitt the object after time t.

So that virtical displacement of stone is 1.25 m

Hotizontal displacement of stone is x = 3 + displacement of object A. 

Initial velocity of object is zero.

so displacement of object is

Since velocity vector inclined at 45º with horizontals.

Add eqn (1) and (2)

from eqn (3) and (4)

From eqn (1) and (2)