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

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

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(We know, 1\ km = 1000\ m ; 1\ hr = 3600\ s)

Given, Initial speed of the bus,u  = 80\ kmh^{-1} = \frac{80\times1000}{3600} = \frac{200}{9} ms^{-1}

The final speed of the bus,v60\ kmh^{-1} = \frac{60\times1000}{3600} = \frac{100}{6} ms^{-1}

Time is taken, t= 5s 

We know, v = u+at

\\ \implies \frac{100}{6} = \frac{200}{9}+a(5) \\ \implies 5a = \frac{900-1200}{6\times9} = \frac{-300}{6\times9} \\ \implies a = -\frac{100}{9} = -1.11\ ms^{-2}

The negative sign implies retardation.

Therefore, the acceleration of the bus is -1.11\ ms^{-2}

Or, the retardation(de-acceleration) of the bus is 1.11 ms^{-2}

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