Question

A bus decreases its speed from 80km h^-1 to 60 km h^-1 in 5 seconds. Find the acceleration of the bus

Answer 1

u = 80 km/h

v = 60 km/h

t = 5 s = 5/3600 h = 1/720 h

Let a be the acceleration of the bus

As v = u + a t

so, 60 = 80 + a × 1/720

or, -20 = a/720

so, a = -20×720 = - 14400 km/h^2

= - 14400×1000/3600×3600 m/s ^2

= -1440/36×36 m/s^2 = - 1.111 m/s^2

_____________________________

Alternate

_____________________________

u = 80 km/h = 80×5/18 m/s = 200/9 m/s

v = 60 km/h = 60×5/18 m/s = 150/9 m/s

t = 5 s

As v = u + a t

so, 150/9 = 200/9 + a × 5

or, -50/9 = a×5

so, a = -10/9 m/s = - 1.111 m/s^2