6. A body is dropped from a height of 300ft with an initial velocity of 30 ft /sec. Assuming no air resistance, (a) find an expression for the velocity of the body at any time t; (b) find the time r(1u1red for the body to hit the ground. 7. A ball is propelled straight up with an initial velocity of 250 ft/sec in a vacuum with no air resistance. How high will it go ?