Question

a car is traveling at a constant velocity.
what can cause the momentum of the car to decrease?
a. an increase in the force pushing the car forward
b. a change in the direction of travel from west to north
c. a net force acting in the opposite direction of the car’s travel
d. an increase in the mass of the car while remaining at constant speed

Explanation:

Step1: Recall the formula for momentum

Momentum \(p = mv\), and according to Newton's second law \(F_{net}=ma=\frac{\Delta p}{\Delta t}\).

Step2: Analyze each option

• Option A: An increase in the force pushing the car forward. If \(F_{net}\) is in the direction of motion, from \(F_{net}=\frac{\Delta p}{\Delta t}\), \(\Delta p> 0\), momentum increases.
• Option B: A change in direction. This changes the direction of momentum (a vector quantity), but does not necessarily decrease its magnitude.
• Option C: A net force acting opposite to the car's travel. From \(F_{net}=\frac{\Delta p}{\Delta t}\), if \(F_{net}<0\) (opposite to the direction of motion), \(\Delta p<0\), momentum decreases.
• Option D: Increase in mass at constant speed. From \(p = mv\), if \(m\) increases and \(v\) is constant, \(p\) increases.

Answer:

C. a net force acting in the opposite direction of the car's travel