A ball is thrown straight up at a speed of 10 m/s and a height of 20 m. If the ball falls all the way to the ground, how long will it take from when it's thrown? How fast will it be going when it hits the ground?

t = 1 + √5  s

t ≈ 3.2 s

v = √500 m/s

v ≈ 22 m/s

Explanation:

Let g = 10 m/s² and UP be the positive direction

s = s₀ + v₀t + ½at²

0 = 20 + 10t + ½(-10)t²

0 = 20 + 10t - 5t²

0 = t² - 2t - 4

Just for fun, lets solve by completing the square

4 = t² - 2t + C

C = b/2

4 + 1 = t² - 2t + 1

5 = (t - 1)²

√5 = t - 1

t = 1 + √5

b) v² = u² + 2gh

v = √(10² + 2(10)(20)) = √500

d

explanation:

v=uf/(u-f)

= 5.10/(5-10) convex lens has positive focal length

=50/-5

=-10 cm (formed at other side)