from the acceleration function s"(t)=(60/(t+1)^2),

Question

 (A) find the acceleration at (t=3sec)?,   (B) find the time when the acceleration is (-15ms^-2)?

Answer 1

(A).  s"(3) = 60/[(4)²] = 60/16 = 3.75 m/sec²

 

(B).  s"(t) = -15        60/(t+1)² = -15

 

                                                60 = -15(t² + 2t +1)

 

                                                15t² + 30t +75 = 0

 

                                                    t² + 2t + 5 = 0

 

                                                   t = (-2 ± √(-16))/2

 

         Since the values of t are not real numbers, there is no time                for which the acceleration is -15 m/sec².