Question #ccfdd

1 Answer
Feb 9, 2016

4 seconds

Explanation:

Using the equation of motion V = U + a*t where
V is the final speed
U is the initial speed
a is acceleration
t is time

The body is travels straight up, slowing down due to gravity, until it reaches a speed of 0 ms^-1 (the apogee) and then accelerates back down to earth in the same time

let gms^-2 be the acceleration due to gravity

Therefore, the time in the initial equation is half the total time, the final speed is 0 and the acceleration is -gms^-2
Substituting these values into the equation
0 = U -gms^-2*1s
Therefore the initial speed is gms^-1

Putting the new value for U (2gms^-1) back into the equation we can solve for t
0 = 2gms^-1 - gms^-2*ts
t = 2 seconds for launch to the apogee, therefore the total time for the second journey is 4 seconds