A small metal ball thrown vertically upwards from the top of a tower with an initial velocity of 20ms-1. If the ball took a total of 6s to reach ground level, determine the height of the tower [g = 10ms-2]
A. 60m B. 80m C. 100m D. 120m
Correct Answer: A
Explanation
Time from tower to top, t = \(\frac{u - v}{g}\) = \(\frac{20 - 0}{10}\) = 2s distance from tower to top x = ut - \(\frac{1}{2}\)gt2 = (20 x 2) - (\(\frac{1}{2}\) x 10 x 2 x 2) = 20m Time from the top to the ground, t = 6 - 2 = 4s distance from top to ground, x = ut - \(\frac{1}{2}\)gt2 = (0 x 4) + (\(\frac{1}{2}\) x 10 x 4 x 4) = 80cm therefore, height of tower = 80 - 20 = 60m
