prove that
Answers
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★ K.E=
2
1
mv
2
\begin{lgathered}\rm 1\ km/h=\dfrac{5}{18}\ m/s\\\\\pink{\bigstar}\ \; \bf 1\ m/s=\dfrac{18}{5}\ km/h\end{lgathered}
1 km/h=
18
5
m/s
★ 1 m/s=
5
18
km/h
\orange{\bigstar}★ Solution \green{\bigstar}★
Mass , m = 800 kg
Kinetic energy , KE = 40,000 J
Velocity , v = ? km/h
Apply formula ,
\begin{lgathered}\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}\end{lgathered}
K.E=
2
1
mv
2
→40,000=
2
1
(800)v
2
→40,000=400v
2
→400=4v
2
→4v
2
=400
→v
2
=100
→v=10 m/s ★
But final answer is in km/h , So ,
\begin{lgathered}\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}\end{lgathered}
→v=10×
5
18
km/h
→v=2×18 km/h
→v=36 km/h ★
So , Option (3) is correct
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