Distance and Motion
St. Mary's HS

 

 

 

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

 

 

Which car has the greater acceleration?

t(sec) t = 0 t = 1 t = 2 t = 3 t = 4 t = 5
Car A 70 m/s 72 m/s 74 m/s 76 m/s 78 m/s 80 m/s
Car B 0 m/s 3 m/s 6 m/s 9 m/s 12 m/s 15 m/s
Car C 90 m/s 90 m/s 90 m/s 90 m/s 90 m/s 90 m/s
Car D 100 m/s 99 m/s 98 m/s 97 m/s 96 m/s 95 m/s

 

 

 

 

 

Car A

 +2 m/s/s

Car B

 +3 m/s/s

Car C

 0 m/s/s

Car D

- 1 m/s/s


t(sec) t = 0 t = 1 t = 2 t = 3 t = 4 t = 5
Car A 70 m/s 72 m/s 74 m/s 76 m/s 78 m/s 80 m/s
Car B 0 m/s 3 m/s 6 m/s 9 m/s 12 m/s 15 m/s
Car C 90 m/s 90 m/s 90 m/s 90 m/s 90 m/s 90 m/s
Car D 100 m/s 99 m/s 98 m/s 97 m/s 96 m/s 95 m/s

 

 

 

 

 

 

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 West
         s
         

 

 

 

(multiply to and bottom by seconds)

 

 

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)

 

 

 

 

 

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