BRAVO! You're right!

Disney's Rockin' Roller Coaster is catapulted from 0 to 60 mi/h in 2.8 s. What is its acceleration? 

We know the speed in mi/h and we know the time in s. Life is far easier if the times involved have the same units. Life is somewhat easier if we stay with a single set of units. Therefore, we will change everything to SI units:

v_i = 0

v = 60 ^mi/_h [ ^{1.61 km}/_mi ] [ ^h/_{60 min} ] [ ^min/_{60 s}] [ ^{1 000 m}/_km ]

v = 26.8 m/s

Now we are ready to "plug into" our equation,

v = v_i + a t

26.8 m/s = 0 + a (2.8 s)

a = ^{26.8 m/s}/_{2.8 s}

a = 9.6 m/s²

Notice that that is nearly equal to the acceleration of gravity!

(c) 2001, Doug Davis; all rights reserved.