A ball is projected vertically upward from the ground. Its height above the ground after t seconds is given by
s(t)=−t3+6t2+15
metres.
(i) Find an expression for the velocity v(t) of the ball at time t seconds.
(ii) Calculate the time at which the ball reaches its highest point.
(iii) Determine the velocity of the ball 1 second after it reaches the highest point.
(iv) Find the acceleration of the ball at the instant it is released and at the highest point.