Calculating Period of a Simple Pendulum with Accelerating Elevator and Truck

[Kawrae]

Okay I thought I understood this, but I guess not... according to this webassign program all my answers are wrong!

>> A simple pendulum is 6.00m long.
(a) What is the period of simple harmonic motion for this pendulum if it is hanging in an elevator that is accelerating upward at 8.00m/s^2?

My attempt: I used the formula T=2pi(L/g)^(1/2). I know the length and for g I first tried just filling in 9.8m/s^2 but that didn't work. So then I tried adding the acceleration in the y direction and got 1.8m/s^2 for g. But that didn't work either. Then I tried just ignoring gravity and using 8.00 that was given but that didn't work either. So now I'm stuck.

(b) What is its period if the elevator is accelerating downward at 8.00 m/s^2?

My attempt: Tried the same as part (a) only using -8.00m/s^2...

(c) What is the period of simple harmonic motion for this pendulum if it is placed in a truck that is accelerating horizontally at 8.00 m/s^2?

My attempt: I used the same formula as part (a) only I figured since it was only moving in the x-direction the 8.00 didn't matter, so I just used 9.8 for g. But it was wrong too.

Please help!

 

[Tide]

Trial and error won't get you very far particularly when there's no one around to tell you whether your answer is correct or not.

HINT: Add up all the forces acting on the mass and equate the sum to the acceleration of the mass.

 

[Kawrae]

Thank you very much I finally figured them all out :)