What is the cause of heat generation in the following situations:
a. We apply brakes on a fast moving car.
b. People often jump up and down to feel warmer in cold weather.

On applying the brakes of care, the kinetic energy of the tire gets converted to heat energy due to the friction between the brakes and the tire surface. Therefore, the friction between the brakes and the road causes heat generation.

(b) People often jump up and down to feel warmer in cold weather

When we are jumping up and down, our heartbeat and blood flow increases. Increased metabolism causes burning of fat and carbohydrates creating energy. This make us feel warmer. Therefore, increased metabolism causes heat generation.