Question

18. An object is thrown downward from an unknown height above the ground with an initial speed of 10 ms-'. It strikes the ground 3.0 s later. What is the initial height (in m) of the object
above ground.​

Answer 1

Answer:

74.1 metres

Explanation:

Given : initial velocity = u = 10m/s    ,    time = t = 3 seconds,       acceleration due to gravity = g = 9.8 m/s²

Let unknown height be 's'.

By Newton's second equation of motion,

s = ut + 1/2gt²

  = 10 * 3 + 1/2 * 9.8 * 9

  = 30 + 44.1

  = 74.1 metres

Answer 2

Answer:   74.1 m

Given :

u = 10m/s    ,  

t = 3 seconds,      

g = 9.8 m/s²

By Newton's second equation of motion,

s = ut + 1/2gt²

 = 10 * 3 + 1/2 * 9.8 * 9

 = 30 + 44.1

 = 74.1 m