Chapter 1.7, Problem 68E

Physical Science Use the height formula in Example 10 to work the given problems. Note that an object that is dropped (rather than thrown downward) has initial velocity $v_0=0$.

A rocket is fired straight up from ground level with an initial velocity of 800 feet per sencond.

(a) How long does it take the rocket to rise 3200 feet?

(b) When will the rocket hit the ground?

EXAMPLE 10 Physical Science If an object is thrown upward, dropped or thrown downward and travels in a straight line subject only to gravity (with wind resistance ignored), the height h of the object above the ground (in feet) after t seconds is given by

$h=-16t^2+v_{0}t+h_0$,

where $h_0$ is the height of the object when $t=0$ and $v_0$ is the initial velocity at time $t=0$. The value of $v_0$ is taken to be positive if the object moves upward and negative it if moves downward.