The height of the stone thrown in air after t secs is expressed by the equation;
H(t) = (63t − 16t²) feet
Velocity is the change in displacement of the body with respect to time.
V(t) = d(H(t))/dt
V(t) = 63 - 32t
To get the time t when the ball will be traveling upward at 15.75 feet per second, we will substitute V(t) = 15.75 into the resulting equation as shown;
15.75 = 63 - 32t
-32t = 15.75-63
-32t = -47.25
t = 47.25/32
t = 1.477seconds
Hence the ball will be travelling upward when t is 1.477s
Explanation: If you look at the line on the graph, you can see that it is going downward, meaning it has a negative slope, and choice b is the only one that has a negative slope
