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:
vi = 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 = vi + 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.