Question

I am unable to understand that how its 5/18 m/s(marked in screenshot above)...plz explain briefly


This is actual question of the solution in screenshot ...
Plz dont solve this below question just explain answer of that above question

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

Answer 1

Answer:

Explanation:

Answer :-

Here, we have

If any thing in the given values are in km/h then we have to first convert it in m/s.

And we do by this by multiplying the value by 5/18.

We take this value because,

We know that,

1 kilometre = 1000 metre

1 hour = 3600 seconds

Given format is km/h

km/h = 1000/3600

m/s = 5/18

or, m/s = 0.28 m/s

Hence, 5/18 we need to convert km/h to m/s.

Example :-

Given :-

Initial velocity, u = 80 km/h = 80 × 5/18 = 22.2 m/s

Final velocity, v = 60 km/h = 60 × 5/18 = 16.7 m/s

Time taken, t = 5 seconds

Acceleration, a = ??

From 1st equation of motion,

we get v = u + at

⇒ a = v - u/t

⇒ a = 16.7 - 22.2/5

⇒ a = - 5.5/5

⇒ a = - 1.1 m/s²

Hence, the acceleration is - 1.1 m/s².

Answer 2

Answer:

$\underline{\bigstar\:\boldsymbol{Conversion\:of\:the\:SI\:Unit :}}$

$:\implies\sf 1km/h=\dfrac{1km}{1h}\\\\\\:\implies\sf 1km/h=\dfrac{1\times 1000m}{1 \times 60min}\\\\\\:\implies\sf 1km/h = \dfrac{1000m}{60 \times 60s}\\\\\\:\implies\sf 1km/h = \dfrac{10m}{36s}\\\\\\:\implies\sf 1km/h = \dfrac{5}{18} m/s$

$\rule{180}{2}$

• Initial Speed (u) = 80 km/h
• Final Speed (v) = 60 km/h
• Time (t) = 5 s

$\underline{\bigstar\:\boldsymbol{According\:to\:the\:Question :}}$

$\dashrightarrow\sf\:\: Acceleration=\dfrac{Final\:Speed-Inital\:Speed}{Time}\\\\\\\dashrightarrow\sf\:\:a=\dfrac{v-u}{t}\\\\\\\dashrightarrow\sf\:\:a=\dfrac{60\:km/h-80\:km/h}{5\:s}\\\\\\\dashrightarrow\sf\:\:a = \dfrac{ - 20\:km/h}{5\:s}\\\\\\\dashrightarrow\sf\:\:a = \dfrac{ - 20 \times \frac{5}{18}\:m/s}{5 \:s}\\\\\\\dashrightarrow\sf\:\:a = - 20 \times \dfrac{5}{18}\:m/s \times \dfrac{1}{5} \:s\\\\\\\dashrightarrow\:\:\underline{\boxed{\sf a = - \:1.1\:m/s^2}}$

⠀

$\therefore\:\underline{\textsf{Hence, Acceleration of the bus is \textbf{- 1.1 m/s ^\text2 }}}.$