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