Question

A train covers 120 m in 5 seconds .what is the speed of the train in km/ hr?

Answer 1

Answer:

$\boxed{\boxed{\underline{\bold{86.4 \: kmh^{-1}}}}}$

Step-by-step explanation:

First method:

Distance = 120 m = 120/1000 km = 12/100 km = 6/50 km = 3/25 km

Time = 5 sec = 5/60 min = 1/12 min = 1/(12*60) hrs = 1/720 hrs

So, Speed in km/h = distance/time

$= \dfrac{3}{25} \div \dfrac{1}{720}\\\\\\= \dfrac{3 \times 720}{25}\\\\\\= \dfrac{3 \times 144}{5}\\\\\\= \dfrac{432 \times 2}{5 \times 2}\\\\\\= \dfrac{864}{10}\\\\\\= \boxed{\boxed{\underline{\bold{86.4 \: kmh^{-1}}}}}$

Second method:

Distance = 120 m

Time = 5 sec

So, Speed in m/s = Distance / time = 120/5 = 24 m/s

Speed in km/h = 24/1000 km ÷ 1/3600 hrs

$= \dfrac{24 \times 3600}{1000}\\\\\\= \dfrac{24 \times 18}{5}\\\\\\= \dfrac{432 \times 2}{5 \times 2}\\\\\\= \dfrac{864}{10}\\\\\\= \boxed{\boxed{\underline{\bold{86.4 \: kmh^{-1}}}}}$

Answer 2

Given ,

Distance = 120 m

Time = 5 sec

In terms of kilometer and hour ,

Distance = 120/1000 km i.e 0.12

Time = 5/3600 hr i.e 0.001388889 hr

We know that ,

$\huge \star \: \: \sf \large\fbox{ \fbox{ Speed = \frac{Distance}{Time} }}$

Substitute the values , we obtain

$\sf \implies Speed = \frac{0.12}{0.001388889} \\ \\ \sf \implies Speed = 86.4 \: \: km/h$

Hence , the speed is 86.4 km/hr (approx)