Math Is Fun Forum

EMPhillips1989

Member

Registered: 2008-01-21

Posts: 40

please help

a ball is thrown vertically upwards with speed 4m/s, neglecting air resistance and taking g=9.8 find the time taken for the ball to return to the ground

right this is my solution:
using newtons second:

integrating this gives:

since

time taken to reach the top is when

at the highest point
t=0.408

does anyone know if i can simply double this to get the total time taken or do i have to integrate again?

Daniel123

Member

Registered: 2007-05-23

Posts: 663

Re: please help

Yes, you can double it.

An easier method would have been to use v = u + at. You know that the speed of the ball when it hits the ground will be the same as the speed when it left. Therefore, taking upwards as positive and downwards as negative:

t = (v-u)/a
  = (-4 - 4)/(-9.8)
  = 0.8163... (which is double your answer)

Last edited by Daniel123 (2008-02-25 03:21:24)