Question

two cars collide at an intersection. one car has a mass of 800 kg and is moving 15 m/s to the north, while the other has a mass of 900 kg and is moving 18 m/s to the south. what is their combined momentum?
a. 28,200 kg·m/s south
b. 4200 kg·m/s south
c. 28,200 kg·m/s north
d. 4200 kg·m/s north

Explanation:

Step1: Define momentum formula

Momentum $p = mv$, where $m$ is mass and $v$ is velocity. Let north - direction be positive and south - direction be negative.

Step2: Calculate momentum of first car

For the first car with $m_1 = 800$ kg and $v_1=15$ m/s, $p_1=m_1v_1 = 800\times15=12000$ kg·m/s.

Step3: Calculate momentum of second car

For the second car with $m_2 = 900$ kg and $v_2=- 18$ m/s, $p_2=m_2v_2=900\times(-18)= - 16200$ kg·m/s.

Step4: Calculate combined momentum

$p_{total}=p_1 + p_2=12000+( - 16200)=-4200$ kg·m/s. The negative sign indicates the direction is south.

Answer:

B. 4200 kg·m/s south