2) A stone is projected downwards with a velocity of 20m/s at an angle of 30degrees below a horizontal line through the point of projection. Find the velocity of the stone after 2 sec.
t=0 => v=20cos30i-20sin30j
V=20cos30i+(-20sin30-9.8t)j
r=20cos30t+(-20sin30t-4.9t^2)j
t=2sec
v=20cos30i+[-20sin30-9.8(2)]j
=17.32i-29.6j
square root of 17.32^2+29.6^2 = 34.29
Horizontal speed: $$V\cos\theta$$ Vertical speed (positive downward): $$V\sin\theta+gt$$ Oblique speed: $$\sqrt{(V\cos\theta)^2+(V\sin\theta+gt)^2}=\sqrt{(20\cos30°)^2+(20\sin 30°+9.81\times2)^2}\approx34.31 m/s$$