Calculating acceleration due to gravity question

[dudforreal]

Homework Statement

An astronaut is standing on Mars. The astronaut throws an object of mass 0.30 kg
vertically upward at an initial speed of 9.0 m/s. It reaches a maximum height of
11 metres.
What is the magnitude of the acceleration of the object?

2. The attempt at a solution

I'm really bad at projectile motion and don't know how to start the question. I know the answer from memory but i don't know how to calculate it using the given information. I tried F=ma but i didn't have the force. I also tried using Newton's 3 equations but time and distance the object landed was missing. Can anyone help in solving this equation?

 

[Mindscrape]

What do you know about an object at the top of its trajectory?

 

[dudforreal]

vertical velocity is zero...?

 

[shyta]

you have initial velocity, final velocity and displacement

 

[dudforreal]

can you show me what equation to use?

 

[Mindscrape]

Right, vertical velocity is zero. Furthermore, do heavier objects fall quicker under gravity? You have more than enough info to answer this question.

 

[a.ratnaparkhi]

It reaches at max. height after traveling 11m. so at that point velocity is zero.
Now you know initial as well as final velocity.And you also know displacement. so you can use third equation of motion to find acceleration.
vf^2=vi^2+2as.

 

[dudforreal]

its max height is 11m, not its displacement at max height

 

[a.ratnaparkhi]

we are considering just vertical quantities. So we can take it as displacement.
According to my method I'm getting acceleration as 3.681 m/s^2.
Is it correct?

 

[dudforreal]

yes. so I got the answer and turns out to be negative. Is it because it is downwards vertical acceleration and we do not include it in the final answer and by the way is mass irrelevant?

 

[shyta]

mass can be considered irrelevant. yes it is negative because acceleration is a vector and we took upwards as positive in our kinematics equation (i.e. positive 11m)

 

[dudforreal]

thanks for the help guys!