Question

When brakes are applied to a moving vehicle, then the kinetic energy of the vehicle is converted to

• A. Potential energy
• B. Mechanical energy
• C. Gravitational energy
• D. Heat energy

Hint:

Braking is an energy transformation process: \[ \text{Kinetic Energy } \left(\frac{1}{2}mv^2\right) \xrightarrow{\text{Frictional Work}} \text{Thermal/Heat Energy } (m_{\text{rotor}} \cdot c_p \cdot \Delta T) \] In modern electric vehicles, regenerative braking systems capture a portion of this kinetic energy, converting it into electrical potential energy stored in batteries rather than losing it entirely as heat.

Answer 1

The Correct Option is D

Braking works purely by friction. When the brake pads or shoes are pressed against the disc or drum, the friction force between the rubbing surfaces resists the wheel's rotation and slows the vehicle down. This friction does not store the vehicle's motion anywhere, it simply dissipates it, and by the principle of conservation of energy, the kinetic energy the vehicle loses cannot disappear, it has to reappear as heat generated at the rubbing surfaces, which is why brake discs get noticeably hot after hard braking. So the kinetic energy of the vehicle is converted to heat energy, option (4).