Aball is tossed upward from a tall building, and its upward velocity v in feet per second, is a function of time t, in seconds, since the ball was thrown. the formula is v(t)=80-32t if we ignore air resistance. express using functional notation the velocity 4 seconds after the ball is thrown and then calculate that value. is the ball rising or falling then?

To calculate the velocity after 4 seconds, just simply use the given equation by substituting t=4 seconds. That would be 

v(4) = 80 - 32(4) = -48 m/s

Velocities are vector quantities. It means that the bearing of the sign matters with respect to the direction of the motion. In conventional terms, negative vectors point downwards or to the left. Positive vectors point upward or to the right. Since the velocity has a negative sign, the ball must be falling downwards.