A rock is projected upward from the surface of the moon, at time t = 0.0 s, with a velocity of The acceleration due to gravity at the surface of the moon is When does the rock reach a height of 180 m above the moon's surface?

17 s

12 s

30 s

23 s

7.5 s

Answer;

7.5 seconds

Explanation;

Given u = initial velocity=30m/sec

a = acceleration on moon=1.62m/s2

h=180m

Using the equation

h = u (t) - 1/2gt² {where g = 1.62 m/s²} and u = 30 m/s

180 = 30t - (0.5) (1.62) t²

0 = 0.81t² - 30t + 180

solving the quadratic equation for the 2 t-values:

t = 7.5 s or t = 30 s

Therefore; the time taken to reach a height of 180 m upwards is 7.5 seconds