Question

a 4,000 - kg truck is traveling north at 8 m/s, and a 1,200 - kg car moves north at 30 m/s. which of the following statements accurately compares the car and truck? a the truck has less inertia than the car. b the truck has less momentum than the car. c the truck has more mass, but less weight than the car. d the truck has more energy than the car.

Explanation:

Step1: Recall inertia concept

Inertia is related to mass. Larger - mass object has more inertia. The truck has a mass of $m_{truck}=4000$ kg and the car has a mass of $m_{car}=1200$ kg. So the truck has more inertia than the car, and option A is wrong.

Step2: Calculate momentum

The momentum formula is $p = mv$. For the truck, $p_{truck}=m_{truck}v_{truck}=4000\times8 = 32000$ kg·m/s. For the car, $p_{car}=m_{car}v_{car}=1200\times30=36000$ kg·m/s. So the truck has less momentum than the car.

Step3: Recall weight concept

Weight $W = mg$. Since $m_{truck}>m_{car}$ and $g$ is the same, $W_{truck}>W_{car}$, so option C is wrong.

Step4: Calculate kinetic - energy

The kinetic - energy formula is $K=\frac{1}{2}mv^{2}$. For the truck, $K_{truck}=\frac{1}{2}\times4000\times8^{2}=128000$ J. For the car, $K_{car}=\frac{1}{2}\times1200\times30^{2}=540000$ J. So the car has more kinetic energy than the truck, and option D is wrong.

Answer:

B. The truck has less momentum than the car.