Solving Newtons 2nd Law Homework: Velocity of Rocket on Ground

AI Thread Summary
The discussion revolves around solving a homework problem related to Newton's Second Law, specifically focusing on the velocity of a rocket. The initial calculations for the rocket's weight and the effects of fuel ejection are confirmed as correct, with a weight of 30N and an initial velocity of 40 m/s for the remaining rocket. For the acceleration during fuel ejection, the calculated value is 200 m/s², leading to a force of 300N upwards. The main question concerns the rocket's velocity in both the east and upward directions, with the conclusion that the eastward velocity is zero due to no horizontal forces, while the upward velocity remains at 40 m/s if gravity is ignored. The discussion highlights the importance of considering gravity in the calculations, suggesting a potential upward velocity of 10 m/s if gravity is factored in.
iuhoosierz
Messages
10
Reaction score
0

Homework Statement


Ok this is kind of long. This is the 4th question on my homework assignment and I need to give background on the first 3 to make sure I got those correct.
1. I am sure on this since it was simply finding the weight of a rocket ship that has an intial mass of 3kg. Answer is 30N

2. Question is: Let's assume half the mass of the rocket is fuel and is spewed out nearly instantaneously. If the fuel for the rocket travels downward at a velocity of 40 m/s then what will be the initial velocity of the rest of the rocket? My answer is 40m/s Is this correct?

3. Instead of saying it is instantaneous let's say that the fuel was ejected in a time of 0.2 seconds.
A. Ignoring gravity during this time, what is the acceleration on the rocket during this time. I used A=change in Vel/Time and got 200 m/s
B. What is the force on the rocket during this time? I used F=MA and got 300N Up

Ok, IF these are all correct here is the question that I cannot figure out.

4. Near the ground there is no wind
A. What is the velocity of the rocket in the East Direction?
B. What is the velocity in the up direction?


Homework Equations





The Attempt at a Solution



I know velocity=change in position/time but not real sure what #'s to use here and really it doesn't make a lot of sense to me. Do I need to use 10m/s for gravity in here somewhere?
Thanks for any help.
 
Last edited:
Physics news on Phys.org
Your answers to 1, 2 and 3 are correct.

4-A. Zero, because there is no horizontal force.
4-B. Doesn't make sense if you ignore gravity. It'll be still 40 m/s.
 
Thanks. So if we weren't ignoring gravity would it be 10m/s?
 
iuhoosierz said:
Thanks. So if we weren't ignoring gravity would it be 10m/s?

How do you arrive at this value?
 
Thread 'Voltmeter readings for this circuit with switches'
TL;DR Summary: I would like to know the voltmeter readings on the two resistors separately in the picture in the following cases , When one of the keys is closed When both of them are opened (Knowing that the battery has negligible internal resistance) My thoughts for the first case , one of them must be 12 volt while the other is 0 The second case we'll I think both voltmeter readings should be 12 volt since they are both parallel to the battery and they involve the key within what the...
Thread 'Correct statement about a reservoir with an outlet pipe'
The answer to this question is statements (ii) and (iv) are correct. (i) This is FALSE because the speed of water in the tap is greater than speed at the water surface (ii) I don't even understand this statement. What does the "seal" part have to do with water flowing out? Won't the water still flow out through the tap until the tank is empty whether the reservoir is sealed or not? (iii) In my opinion, this statement would be correct. Increasing the gravitational potential energy of the...
Back
Top