Hey all, I am a little confused on this, I was trying to study and these two questions came up... I guess i am confused, I don't know the solutions and I want to know which it is and why... 1. A helium balloon is observed to rise up into the air at the front of the classroom, and is only being held to the ground by a rock. the professor pours liquid nitrogen (77K) onto the balloon. The balloon suddenly drops to the ground. The change in which property of the helium gas caused the balloon to no longer be bouyant? A. Pressure B. Volume C. Temperature D. Mass E. None of the above A pendulum undergoing simple harmonic motion can be described by the expression: X(t) = .2 sin(π t - .3). what is the magnitude of the maximum angular acceleration of this pendulum? A. .2 1/s^2 B. .2/π 1/s^2 C. .2π 1/s^2 D. .2π^2 E. none of these. I have been trying to review these two questions for a while and could use some help. I feel like 1. should be mass pouring nitrogen onto the balloon, but I was told that was wrong. 2. I said none of these, because I don't know what s is, and on top of that its just two derivatives of the X.