Estimating Decelerating Forces Flashcards

All 6 cards in this deck

What energy transfer happens when the brakes of a vehicle are applied?

Work done by the friction force between the brakes and the wheel reduces the kinetic energy of the vehicle and increases the internal (thermal) energy, so the brakes' temperature rises.

What are the dangers of a very large deceleration when braking?

The brakes may overheat and/or the driver may lose control of the vehicle (skidding).

To stop a vehicle within a certain distance, how does the braking force needed depend on the vehicle's speed?

The greater the speed, the greater the braking force needed.

What are the steps to estimate the braking force on a car using energy?
e.g. a $1000$ kg car travelling at $10$ m/s stops in $25$ m

1. Find the kinetic energy: $\frac{1}{2} \times 1000 \times 10^2 = 50\,000$ J
2. Work done by the brakes equals this energy: $F \times d = 50\,000$ J
3. $F = 50\,000 \div 25 = 2000$ N

What are the steps to estimate the braking force from a vehicle's deceleration?
e.g. a $1200$ kg car decelerates at $5$ m/s$^2$

1. Use $F = m\,a$
2. $F = 1200 \times 5 = 6000$ N (acting backwards on the car)

True or false? A greater braking force produces a greater deceleration of the vehicle.

True. Larger decelerations can cause the brakes to overheat or the driver to lose control.