# Answer to Question #43722 in Atomic and Nuclear Physics for mira

Question #43722

A bus is moving at 10ms^-1 towards a traffic light.when the driver sees the light changed to red,the bus is at a distance of 20m.the reaction time of driver us 0.5s and the deceleration is 4.5ms^-2.with the brake fully applied,how far is the bus when stops?

Expert's answer

Time of driver's reaction is 0,5 s. Hence, the distance tothe light when the bus will actually start to brake is 20-10*0.5=15m

Also we need to find a time to stop thebus. v=a*t. 10=4.5*t,t=20/9s

Now, we can calculate the distance travelled after theapplication of brake: S=v*t-a*t^2/2=10*20/9-(4.5/2)*(20/9)^2=11(1/9)m

So, the distance is: 15-11(1/9)=3(8/9)m=3.889 m

Also we need to find a time to stop thebus. v=a*t. 10=4.5*t,t=20/9s

Now, we can calculate the distance travelled after theapplication of brake: S=v*t-a*t^2/2=10*20/9-(4.5/2)*(20/9)^2=11(1/9)m

So, the distance is: 15-11(1/9)=3(8/9)m=3.889 m

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