Which of the following statements about permafrost is true? choose one: a. it can extend as deep as 1,500 km below ground surface. b. permafrost that thaws and refreezes produces a pentagonal or hexagonal ground surface pattern called columnar joints. c. it is rare in periglacial environments. d. it can melt to a depth of a few meters in summer, then refreeze in winter.

The image shows the positions of a car on a roller coaster track. arrange the cars in order based on their gravitational potential energy. begin with the lowest potential energy and end with the highest.

Erosion of the beach is normally a slow process. however, in certain situations, large chunks of shore may wash out to sea. what could cause this to happen?

Aperson stands on a platform, initially at rest, that can rotate freely without friction. the moment of inertia of the person plus the platform is ip. the person holds a spinning bicycle wheel with its axis horizontal. the wheel has moment of inertia iw and angular velocity ωw. take the ωw direction counterclockwise when viewed from above. part a what will be the angular velocity ωp of the platform if the person moves the axis of the wheel so that it points vertically upward?