Question

imagine you are driving a car down the road next to a large 18 - wheel semi - truck. both of you are traveling at the same speed, and traffic in front of you stops suddenly. which natural law of driving explains why you will be able to stop before the semi - truck can?
a doppler effect
b momentum
c kinetic energy
d centrifugal force

Explanation:

• Doppler effect: It is related to the change in frequency of waves due to the relative motion of the source and the observer. It has nothing to do with stopping a vehicle.
• Momentum: The formula for momentum is \(p = mv\) (where \(m\) is mass and \(v\) is velocity). A semi - truck has a much larger mass than a car. When both are moving at the same speed \(v\), the semi - truck has a larger momentum (\(p_{truck}=m_{truck}v\) and \(p_{car}=m_{car}v\), \(m_{truck}\gg m_{car}\)). To stop, a force is applied over a time (\(F\Delta t=\Delta p\)). A larger momentum change (\(\Delta p\)) for the truck means it will take more time (or a larger force, which is usually limited by tire - road friction) to stop.
• Kinetic energy: The formula for kinetic energy is \(K=\frac{1}{2}mv^{2}\). While a truck has more kinetic energy, the key concept related to stopping (when considering forces and time) is more directly related to momentum (from \(F = \frac{\Delta p}{\Delta t}\)) rather than just kinetic energy (\(W=\Delta K\), where \(W = Fd\) is work - energy, and it is more about distance \(d\) and force \(F\) in a different context compared to the force - time - momentum relation).
• Centrifugal force: It is a pseudo - force in a rotating reference frame. It is not relevant to the linear stopping of vehicles on a straight road.

Answer:

B. momentum