Distance and Motion St. Mary's HS

 

C. Acceleration - time rate of change in velocity (how quickly velocity is changing)

 

 

2 ways to have zero acceleration

 

a) remain at rest

 

b) constant velocity

 

1. Equation

 

a = ∆V/∆t = (Vf - Vi)/t

Ex 1

Starting Velocity: 5m/s West

Final Velocity: 25 m/s West

Time during speed change: 5 secs

 

a = (Vf - Vi)/(tf -ti)

 

a = 20 m/s W/5 sec

 

= 4 m/s/s West

 

or 4 m/s2 West

 Ex 2)

 

Starting Velocity: 20m/s West

    Final Velocity:5 m/s West

     Time: 5 seconds

 

 

 

a = (Vf - Vi)/(tf -ti)

 

 

 a = -15m/s W/5 seconds =

        

= - 3 m/s/s West  

 

 

or -3 m/s2  W

 

or 3 m/s2 East


Object is said to be  

'accelerating backwards'

 

(Because the force required to slow an object always opposes the objects motion)