An object dropped from rest almost infinitely far from earth falls to earth because of earth's gravitational field, and strikes the surface with a speed of about
a. 8 km/s
b. 9.8 m/s
c. 11 km/s
d. none of the above

If a rock is thrown upward on the planet mars with a velocity of 12 m/s, its height (in meters) after t seconds is given by h = 12t − 1.86t2. (a) find the velocity of the rock after two seconds. m/s (b) find the velocity of the rock when t = a. 12−3.72a m/s (c) when will the rock hit the surface? (round your answer to one decimal place.) t = s (d) with what velocity will the rock hit the surface? m/s