Calculate the kinetic energy of a car of mass $750 \,kg$ moving with a velocity of $54 \,km \cdot h^{-1}$. Find the new kinetic energy of the car if a passenger of mass $50 \,kg$ sits in the car.

(N/A) Given: Mass of car $m_1 = 750 \,kg$,Velocity $v = 54 \,km \cdot h^{-1} = 54 \times \frac{5}{18} \,m \cdot s^{-1} = 15 \,m \cdot s^{-1}$.
Initial Kinetic Energy $(KE_1)$:
$KE_1 = \frac{1}{2} m_1 v^2 = \frac{1}{2} \times 750 \times (15)^2 = 375 \times 225 = 84375 \,J$.
When a passenger of mass $50 \,kg$ sits in the car,the new total mass $m_2 = 750 \,kg + 50 \,kg = 800 \,kg$.
New Kinetic Energy $(KE_2)$:
$KE_2 = \frac{1}{2} m_2 v^2 = \frac{1}{2} \times 800 \times (15)^2 = 400 \times 225 = 90000 \,J$.