Question

abus increases its speed from 36 kilometre per hour to 90 km per hour in 10 seconds and stops in 5 seconds after applying brakes calculate acceleration in both cases

Answer 1

36km/hr = 10m/s

90km/h = 25m/s

here v = 25m/s

u= 10m/s

t = 10sec

so a = v-u/t


a = 25-10 / 10

a= 1.5m/s square.

2nd

here v =0

u = 25m/s

t = 5 sec

so a = v-u/t

so a = 0-25/ 5

so a = -5 m / s square

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Answer 2

case 1-
______________

u = 36 km/h

= 36 × 5/18 m/s = 10m/s

v = 90km/h

= 90× 5/18 m/s = 25m/s

time = 10s

By the first eq. of motion ,
v = u + at

==> a = (v - u )/t
= (25 - 10)/10 m/s^2
= 15/10 m/s^2
= 1.5 m/s^2




case 2-
______________

u = 25m/s

v = 0 ( since, after applying brakes the bus comes at rest)

t = 5s

a = (v - u)/t
= (0 - 25)/5 m/s^2
= - 25/5 m/s^2
= -5 m/s^2
therefore, retardation (negative acceleration) = 5m/s^2

hope this helps.....

with regards....
#Misa