Acceleration

acceleration (a or )• the rate of change of speed or velocity

positive acceleration• the object is increasing its speed or velocity

negative acceleration• the object is decreasing its speed or velocity

= + at

= - at

a – acceleration (m/s2, km/h2)v2 – final velocity (m/s, km/h)v1 – initial velocity (m/s, km/h)t – time (s,h)

Terms that replace numbers in questions:

Starts from rest v1 = 0

Comes to a stop v2 = 0

Falling towards the ground a = 9.81 m/s2

Constant speed a = 0

***if the acceleration and the velocity have different signs (+ or -) or direction (N or S), this indicates that the object is slowing down or decelerating

Demonstration

Units

Acceleration is measured in m/s2 or km/h2.

1. A student is travelling at 16.0 m/s [N] and 3.0 seconds later is travelling at 4.0 m/s [N]. Find the acceleration of the student.

[N] = +ve

= 16.0 m/s = 4.0 m/st = 3.0 s

= ?

=

= -4

\ the student is decelerating at 4.0 m/s2 [S]

2. A student is driving at 60.0 km/h. She accelerates at 2.0 km/h2 for 45.0 minutes. What is her final speed?

v1 = 60.0 km/ha = 2.0 km/h2

t = 45 min. = 45/60 = 0.75 h

v2 = ?

(.75) 2 = (.75)

1.5 = - 60

60 + 1.5 = - 60 + 60

= 61.5

\the final speed of the student is 62 km/h.

1.4 Prac. #5-8