A small metal ball is thrown vertically upwards from the top of a tower with an initial velocity of 20m/s. If the ball took a total of 6 seconds to reach the ground level, determine the height of the tower

John Perolski
August 21, 2023

Physics Jamb, Waec, Neco Past Questions & Answers on Speed, Velocity and Acceleration

QUESTIONS 44.  A small metal ball is thrown vertically upwards from the top of a tower with an initial velocity of 20m/s. If the ball took a total of 6 seconds to reach the ground level, determine the height of the tower (g=10m/s²).

  • A. 60m
  • B. 80m 
  • C. 100ms
  • D. 120m 

JAMB 1991 Ans: 20m


SOLUTIONS 

  • Acceleration due to gravity g,=>10m/s²
  • Initial velocity u, 20m/s
  • Final velocity v, = 0m/s
  • Total time taken = 6s 

  • Time from tower to top, t = u−v/g
  • t= 20−0/10
  • t = 2s


Distance from tower to top

h = ut - ½gt²

h = (20 x 2) - (½ x 10 x 2 x 2)

h = 20m


Time from the top of tower to the ground, 

t = 6-2

t = 4s


Distance from top of tower to ground,

h = ut - ½gt²

h= (0 x 4) + (½ x 10 x 4 x 4)

h= 80cm


Therefore, the height of the tower = 80 - 20

h = 60m