Acceleration of free falling object on planet X

[1irishman]

Homework Statement

While on planet X, an object is thrown vertically upward with an initial velocity of 5m/s. If this object returns to the point of release in 3s, what is the acceleration of a free falling object on this planet?

Homework Equations

a=vf-vi/t

The Attempt at a Solution

0-5/3
= -1.6m/s^2

The answer is -3.3m/s^2 in the book...i don't understand how they arrived at that?

 

[rl.bhat]

Hi 1irishman, welcome to PF.
vf is zero when the object reaches the maximum height.
What is the time taken by the object to reach that point?

 

[1irishman]

1.5s

 

[1irishman]

thank you rl...i see now.