Which of the following are mechanical waves?
A. waves that travel in empty space
B. sound and ocean waves
C. light waves
D. x-rays

The consumption of fossil fuels could be

Which of the following situations is impossible? a) an object has velocity directed east and acceleration directed east. b) an object has zero velocity but non-zero acceleration. c) an object has constant non-zero velocity and changing acceleration. d) an object has velocity directed east and acceleration directed west. e) an object has constant non-zero acceleration and changing velocity.

Which planet do you think would be easiest for humans to colonize some day?