Question

An athlete runs 400 metres race in 50 seconds. what is the speed of the athlete in km / hr​

Answer 1

${\pmb{\underline{\sf{ Required \ Solution ... }}}}$

• Distance = 400 metres
• Time = 50 seconds

Speed is directly proportional to the Distance & Time.

$\circ \ {\pmb{\underline{\boxed{\sf{ Speed = \dfrac{Distance}{Time} }}}}} \\ \\ \\ \colon\implies{\sf{ \cancel{ \dfrac{400}{50} } }} \\ \\ \\ \colon\implies{\sf{ 8 \ m/s _{ \green{(Speed)} } }}$

${\pmb{\underline{\sf{ The \ Speed \ of \ an \ athlete \ is \ 8 \ m/s . }}}}$

~For conversion of speed into km/hr from m/s as to multiply by 18/5 that:-

$\colon\implies{\sf{ 8 \times \dfrac{18}{5} }} \\ \\ \colon\implies{\sf{ \cancel{ \dfrac{144}{5} } }} \\ \\ \colon\implies{\underline{\boxed{\sf{ 28.8 \ km/hr _{(Speed)} }}}}$

Hence,

${\pmb{\underline{\sf\red{ The \ Speed \ of \ an \ athlete \ is \ 28.8 \ km/hr . }}}}$

${\pmb{\underline{\sf{ More \ to \ Know ... }}}}$

• Time: seconds(s), minutes (min), hours (hr)

• Distance: (meters (m), kilometers (km), miles, feet

• Speed: m/s, km/hr

• To convert from km / hour to m / sec, we multiply by 5 / 18. So, 1 km / hour = 5 / 18 m / sec.
• To convert from m / sec to km / hour, we multiply by 18 / 5. So, 1 m / sec = 18 / 5 km / hour = 3.6 km / hour.