• Support PF! Buy your school textbooks, materials and every day products via PF Here!

Impulse question.

  • Thread starter j_suder2
  • Start date
1. The problem statement, all variables and given/known data

Hail stones of mass 0.0650 kg are falling straight down with a speed of 15 m/s when they strike a car roof. If the hailstones bounce to a height of 12 cm above the car, what is the impulse that the car roof imparts to a single hailstone?

2. Relevant equations
p=mv J=Ft


3. The attempt at a solution
I tried finding the downward momentum first and then equalling it to the upward momentum of the hailstones but I am stuck on where to plug in the height of the bounce.
Do I need to find velocity or time of the hailstone on the way up first? If I found time I think I could multiply it by Force to get J (Impulse).
 

Dick

Science Advisor
Homework Helper
26,255
618
Find the velocity up and then use p=mv, J=delta(mv) where delta means the difference between down and up (don't forget one is negative relative to the other). Velocity up isn't equal to velocity down. The lost energy goes into denting the car roof.
 
Thank you,
I am still not sure how to find v, we have not done any of these type of questions in class.
I have tried making both sides equal to the minus of the other, but come up with the same (15m/s) because the mass is the same. Time is also unknown so I'm not sure.
I tried to find the original height by equalling momentum on either side and came up with 0.76 meters. I used this to determine the time to fall as 0.05 s. From this I just now found the velocity up as 2.4 m/s. Now, using the info you gave me, initial p=.975 and final p=-.156.
so delta p=1.13 kg*m/s. The answer is 1.07 so I'm not sure if this is the way to do this.
 

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving
Top