Helge, Steve, and Heidi are sitting on a sled on a slope covered with a hard snow. The sled is stationary. The friends have different suggestions for how to make the sled start moving: Helge: If one of us gets off, the sled will start moving.
Steve: We should invite another person to join us, and then the sled will start moving.
Heidi: We should get off the sled, polish the bottom of the sled to make it smoother, and sit back down on it. The sled will then start moving.
Who suggests the correct solution? Select the correct equation for acceleration ax along the incline. Assume the x-axis is directed down along the incline, and the y-axis is directed normal to the incline. Let μs and θ denote the coefficient of static friction and the angle the incline makes with the horizontal, respectively.