Question

6.
A car accelerates uniformly from 0 to 72 km/h in 11.5 seconds.
[a] What is the acceleration ofo the car in m/s ?
[b] What is the position of the car by the time it reaches the velocity of 72km/h?
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Answer 1

Answer:

(a) acceleration=6.26 m/s

(b) Position=6.25 m

Answer 2

Answer: a) The acceleration a is a measure if the rate of change of the velocity within a period of time. Hence 

u =  

change in velocity

change in time

=  

v - u

t

=  

72 km/h - 0

11.5 seconds

We now convert 72 km/h into m/s

u = 72 km/h =  

72 * 1km

1 hour

 

1000 m

1 km

 

1 hour

3600 seconds

= 20 m/sWe now calculate the acceleration a 

a = (20 m/s) / (11.5 s) = 1.74 m/s2 (approximetd) 

b) Two ways to find the position x: 

1) x = (1/2)(v + u) t        or        2) x = (1/2) a t 2 + u t 

1) We first use: x = (1/2)(v + u) t = 0.5*(20 m/s + 0)*11.5 = 115 m 

2) We now use: (1/2) a t2 + u t = 0.5*1.74*(11.5) 2 + 0*t = 115 m