Question

3.2.2 quiz: momentum
question 4 of 10
two billiard balls, each with a mass of 0.17 kg, collide with each other on a pool table. before the collision, one ball is moving north at 2.8 m/s and the other ball is moving south at 1.6 m/s. what is the momentum of this system after the collision?
a. 0.74 kg·m/s north
b. 0.20 kg·m/s south
c. 0.74 kg·m/s south
d. 0.20 kg·m/s north

Explanation:

Step1: Define north - south direction

Let north be the positive direction and south be the negative direction.

Step2: Calculate initial momentum of first ball

The momentum formula is $p = mv$. For the first ball with $m = 0.17$ kg and $v=2.8$ m/s, $p_1=0.17\times2.8 = 0.476$ kg·m/s.

Step3: Calculate initial momentum of second ball

For the second ball with $m = 0.17$ kg and $v=- 1.6$ m/s, $p_2=0.17\times(-1.6)=-0.272$ kg·m/s.

Step4: Calculate total initial momentum

According to the law of conservation of momentum, the total initial momentum $p_{total}=p_1 + p_2=0.476+( - 0.272)=0.204\approx0.20$ kg·m/s. Since the result is positive, the direction is north. And the total momentum after the collision is equal to the total initial momentum.

Answer:

D. 0.20 kg·m/s north