Avolcanic eruption melts a large area of rock, and all gases are expelled. after cooling, 40ar (atomic number 18) accumulates from the ongoing decay of 40k (atomic number 19) in the rock (t1/2 = 1.25 × 109 yr). when a piece of rock is analyzed, it is found to contain 1.33 mmol of 40k and 1.50 mmol of 40ar. how long ago did the rock cool? enter your answer in scientific notation.

Your starship, the aimless wanderer, lands on the mysterious planet mongo. as chief scientist-engineer, you make the following measurements: a 2.50-kg stone thrown upward from the ground at 14.0 m/s returns to the ground in 5.70 s ; the circumference of mongo at the equator is 2.20×10^5 km ; and there is no appreciable atmosphere on mongo. (a) the starship commander, captain confusion, asks for the following information: what is the mass of mongo? (b) if the aimless wanderer goes into a circular orbit 2.20×10^4 km above the surface of mongo, how many hours will it take the ship to complete one orbit? (c) an unmanned spacecraft is in a circular orbit around the moon, observing the lunar surface from an altitude of 44.0 km . to the dismay of scientists on earth, an electrical fault causes an on-board thruster to fire, decreasing the speed of the spacecraft by 23.0 m/s . if nothing is done to correct its orbit, with what speed (in km/h) will the spacecraft crash into the lunar surface?