Introductory physics: Time for a ball thrown vertically to reach maximum height

[danielsmith123123]

Homework Statement

A 3 kg ball is thrown vertically into the air with an initial velocity of 15 m/s. What is the time it takes for the ball to reach its maximum height?

Relevant Equations

Vf =vi +at
Vf^2 = Vi^2 +2ax
x = Vf t - (1/2)(a)(t^2)
x = Vi t + (1/2)(a)(t^2)

Is the answer key wrong? I keep getting the same answer and it is verified with the freefall equation distance=1/2 (g)(t^2)

 

[nasu]

You should write the full text of the problem, not an abstract of it. Where did the value of d comes from?

 

[danielsmith123123]

Ok thank you, i edited the forum. I guess you can't open pictures on this website, but i calculated d with Vf^2=Vi^2 +(2)(a)(d)
0^2 = 15^2 + (2)(-9.8)d
d = 11.4m
(I realize i probably shouldn't use "x" and "d" interchangibly)

 

[kuruman]

You found the maximum height. The problem is asking you to find the time it takes to reach that maximum height. Your answer should be a number in seconds, not meters.

 

[nasu]

Ok thank you, i edited the forum. I guess you can't open pictures on this website, but i calculated d with Vf^2=Vi^2 +(2)(a)(d)
0^2 = 15^2 + (2)(-9.8)d
d = 11.4m
(I realize i probably shouldn't use "x" and "d" interchangibly)

You don't need the height but you got it OK. What is your problem? I cannot read the image you posted. It is not clear enough.