The height of a projectile launched into the air is given by h (t)= -16t^2 + 48t + 60, where h is the height of the projectile in feet above the ground and t is the number of seconds after its launch. Find the *instantaneous rate of change* in the height of the projectile at 1.5 seconds. It is supposed to be 24 feet per second. Isn't it just -32t + 48 and then putting the 1.5 in for that t?

Question

The height of a projectile launched into the air is given by h (t)= -16t^2 + 48t + 60, where h is the height of the projectile in feet above the ground and t is the number of seconds after its launch.  Find the *instantaneous rate of change* in the height of the projectile at 1.5 seconds.  It is supposed to be 24 feet per second.  Isn't it just -32t + 48 and then putting the 1.5 in for that t?

bobpursley · Accepted Answer

h(t)=-16t^2 + 48t + 60 dh/dt=-32t+48, at t=1.5, then h'=0 you are right.

Steve · Answer

yes, but dh/dt=0 at t=1.5 Don't know how they get 24. dh/dt=24 at t=3/4