A stone is thrown upwards from the roof with a velocity 15ms^-1 at an angle 30degree to the horizontal. The height of the building is 40m.calculate the magnitude of the velocity of the stones before it strikes the ground.

Answer 1

Yo = 15*sin30 = 7.5 m/s. = Ver. component of initial velocity.

Y^2 = Yo^2 + 2g*h = 0.
h = -Yo^2/2g = -(7.5)^2/-19.6 = 2.87 m.
above the roof.

V^2 = Vo^2 + 2g*(h+40) = 0 +19.6*42.87 = 840.25
V = 29 m/s.