A roller coaster is pulled up to the top of a hill 45 m high. The cart then moves over the crest at an average speed of 0.5 m/s before it plunges down to its lowest point, 5 m above the ground. From there, it climbs over a second hill only 15 m high. What is the cart’s speed as it goes over the top of the second hill?

Adiver named jacques observes a bubble of air rising from the bottom of a lake (where the absolute pressure is 3.50 atm) to the surface (where the pressure is 1.00 atm). the temperature at the bottom is 4.00 ∘c, and the temperature at the surface is 23.0 ∘c. what is the ratio of the volume of the bubble as it reaches the surface (vs) to its volume at the bottom (vb)? if jaques were to hold his breath the air in his lungs would be kept at a constant temperature. would it be safe for jacques to hold his breath while ascending from the bottom of the lake to the surface?