Question

1. the illustration above shows a student about to throw a ball while standing on a skateboard. which illustration below shows the skateboards direction of motion after the student releases the ball?
2. which is true about the speeds of the skater and the ball after release?

a. the skater is faster since they are bigger
b. the ball is faster since its smaller
c. they have the same speed, since momentum is conserved
e.

1. which has more momentum: a 12 kg ball rolling at 12 m/s or a 15 kg ball rolling at 10 m/s?

Explanation:

Step1: Analyze the direction of motion (Question 16)

According to Newton's third law, when the student throws the ball in one direction (left as per the initial arrow), there is an equal and opposite reaction. So the skateboard will move in the opposite direction (right).

Step2: Analyze the speeds (Question 17)

Momentum \(p = mv\). Initially, the total momentum of the system (student + skateboard + ball) is zero (assuming at rest). After release, \(m_{skater}v_{skater}+m_{ball}v_{ball}=0\), so \(v_{skater}=-\frac{m_{ball}}{m_{skater}}v_{ball}\). Since \(m_{skater}>m_{ball}\), \(|v_{ball}| > |v_{skater}|\).

Step3: Calculate momentum (Question 18)

For the first ball: \(p_1=m_1v_1 = 12\times12=144\space kg\cdot m/s\)
For the second ball: \(p_2=m_2v_2=15\times10 = 150\space kg\cdot m/s\)

Answer:

1. C
2. b
3. The 15 kg ball rolling at 10 m/s has more momentum.