Question

A train moving with a speed of 180 kmhr-1
suddenly stops by applying brakes.
Calculate the time it will take to stop by travelling a distance of 20m before stopping.

Answer 1

Given that,

Acceleration a=−0.5m/s  

Speed v=180km/h

Using equation of motion,  

v=u+at

Where,  

v = final velocity

u = initial velocity

a = acceleration

t = time

Put the value into the equation

Finally train will be rest so, final velocity,v=0

0=25−0.5t

25=0.5t

t=  

0.5

25

t=50 sec

Again, using equation of motion,  

S=ut+  

2

1

​ at  

2

 Where, s = distance

v = final velocity

u = initial velocity

a = acceleration

t = time

Put the value into the equation

Where S is distance travelled before stop

s=25×50−  

2

1

×0.5×(50)  

2

s=1250 m                                          

So, the train will go before it is brought to rest is 1250 m.

Hence, A is correct.

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