Question

A Car of mass 800 kg is moving with a velocity 72 km/h. By applying brake, the velocity of car become 18 km per hour in 10 secends calculates the work done by the brake ​

Answer 1

Given :-

m = 800kg

u = 72 kmph = 72 * 5/18 = 20 m/s

v = 18 kmph = 18 * 5/18 = 5 m/s

t = 10s

Work done by it = ?

Solution :-

First, we need to find the retardation of the car.

→ v = u + at

→ 5 = 20 + a (10)

→ 10a = - 15

→ a = -3/2

• $\bf{We\: know \:a\:formula\:\:\rightarrow\:\:v^2-u^2=2aS$

$\bf{\rightarrow\:\:v^2-u^2=2aS$

$\bf{\rightarrow\:\:5^2-20^2=2(\frac{-3}{2}) S$

$\bf{\rightarrow\:\:25-400=(\frac{-3}{1}) S$

$\bf{\rightarrow\:\:-375=({-3}{}) S$

$\bf{\rightarrow\:\:S = \frac{-375}{-3}$

$\bf{\rightarrow\:\:S = \frac{375}{3}$

$\bf{\rightarrow\:\:S = 125m$

We know that,

$\bf{\rightarrow\:\:Work\:done=Force*S$

But F = mass * a

So, we get

$\bf{\rightarrow\:\:Work\:done=mass*a*S$

$\bf{\rightarrow\:\:Work\:done=800(\frac{-3}{2}) 125$

$\bf{\rightarrow\:\:Work\:done=400(\frac{-3}{1}) 125$

$\bf{\rightarrow\:\:Work\:done=50,000(-3)$

$\bf{\rightarrow\:\:Work\:done=-1,50,000\:Joules$

$\bf{\rightarrow\:\:Work\:done=-150\:\:Kilo\:Joules$

$\bf{\rightarrow\:\:Work\:done=-150\:kJ$

Final Answer :-

$\bf{\rightarrow\:\:Work\:done=-150\:kJ$

_________________________________________________

Thank you, please mark as brainiest!

$\bf{\rightarrow\:\:ANAGH\:$ :)