Question

Find the velocity of a motor car of mass 800kg, if its kinetic energy
is 40,000 joule:
(a) 63 Km/hr
(b) 50 Km/hr
(c) 36 Km/hr
(d) 1/50 Km/hr​

Answer 1

Answer:

1/2 mv^2 = K

1/2 * 800 * v^2 = 40000

v^2 = 40000*2/800

v^2 = 100

v = 10 m/s

10*18/5 = 36 km/h

hope it helps ........

pls mark brainliest

Answer 2

Velocity of the motor car is 36 km/h

Option (3)

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$\orange{\bigstar}$  Given  $\green{\bigstar}$

Mass of the motor car is 800 kg

It's Kinetic energy is 40,000 Joules

$\orange{\bigstar}$  To Find  $\green{\bigstar}$

Velocity of the motor car

$\orange{\bigstar}$  Key Points  $\green{\bigstar}$

$\pink{\bigstar}\ \; \bf K.E=\dfrac{1}{2}mv^2$

$\rm 1\ km/h=\dfrac{5}{18}\ m/s\\\\\pink{\bigstar}\ \; \bf 1\ m/s=\dfrac{18}{5}\ km/h$

$\orange{\bigstar}$  Solution  $\green{\bigstar}$

Mass , m = 800 kg

Kinetic energy , KE = 40,000 J

Velocity , v = ? km/h

Apply formula ,

$\bf K.E=\dfrac{1}{2}mv^2\\\\\to \rm 40,000=\dfrac{1}{2}(800)v^2\\\\\to \rm 40,000=400v^2\\\\\to \rm 400=4v^2\\\\\to \rm 4v^2=400\\\\\to \rm v^2=100\\\\\to \bf v=10\ m/s\ \; \pink{\bigstar}$

But final answer is in km/h , So ,

$\to \rm v=10\times \dfrac{18}{5}\ km/h\\\\\to \rm v=2\times 18\ km/h\\\\\to \bf v=36\ km/h\ \pink{\bigstar}$

So , Option (3) is correct

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