velocity and displacement

Question

A ball is thrown from ground level with a velocity of 24.5 meters per second. As it starts back down to the ground, it hits a tree at a point 29.4 meters from the ground. How many seconds is the ball in the air before it hits the tree? Use h = vt – 4.9t2 in your work.

Answer 1

h=vt – 4.9t^2

29.4=24.5t-4.9t^2

4.9t^2-24.5t+29.5=0

t=24.5+sqrt(24.5^2-4(4.9)(29.5))/(2*4.9)

 =24.5+4.696/(9.8)

 =2.979

 =3 (Approx)