# 8. An object A is kept fixed at the point x = 3 m and y = 1.25 m on a plank P raised 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 vector 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 vector u and the time after which the stone hits the object. Take g = 10 m/s2.

aku -- kumar
38 Points
12 years ago

dear student,

solving on the pc is not possible you can buy arihant books to see the solutions or go to resonance website and place a order for rank master there you'll get the solutions.........its price is Rs.750, or check some old books from your seniors

bhanuveer danduboyina
95 Points
12 years ago

It is a big question but the answer is rather easy

aku -- kumar
38 Points
12 years ago

see rel vel of ball w.r.t trolley,

v(rel)=vcosψ i+ v sinψ j -(root{3}-1)j

say if some φ anghle is made by this vector

so tan φ = v sinψ - ( root3-1)/vcosψ.    ........(1)

as the ball hits the trolley so the relative velocity is towards trolley; as a result the angle made by vel vector of ball w.r.t trolley is 45 with +ve X-axis

if ψ=4Θ/3, keep this value in(1). at t=0 & φ= 45  solve the equation and get the value of v which is 2m/s at 60 degree to X-axis