Question

A truck running at 90 km/h is brought to rest over a distance of 25m. calculate the retardation and time for which brakes are applied

Answer 1

Speed =90km/h=25m/s
Distance = 25m
0-625=50a
a=-12.5m/s^2
0=25-12.5t
t=250/125=4sec

Answer 2

Step-by-step explanation:

A truck travelling at 90 km/h is brought to a stop over a distance of 25 m. What is the retardation (negative acceleration/time of brake application)?

Initial velocity u = 90 km/h =25 m/s

Final velocity v = 0 m/s (brought to rest)

Distance travelled s in coming to rest = 25 m

Using the relation,

v² - u² = 2 a s, where a is the acceleration

0² - 25² = 2 . a . 25,

a = - ( 625/50) = - 12.5 m/s². The retardation is 12.5 m/s² ( negative sign in a implies it is retardation).

From a we can calculate time for which brakes were applied.

u = 25 m/s

v = 0 m/s

a = - 12. 5 m/s²

Using the relation, v = u + a t,

Substituting various values, we get

0 m/s =2 5 m/s - 12.5 m/s² t s

t = 2 s.

So brakes are applied for 2 s.