Calculating Jet Engine Thrust: How to Use Newton's Second Law

  • Thread starter Thread starter chrishere?
  • Start date Start date
  • Tags Tags
    Hi
AI Thread Summary
A jet engine generates thrust by taking in air, compressing it, and ejecting it at high speed. To calculate thrust, one must apply Newton's Second Law, focusing on the rate of change of momentum rather than velocity alone. The discussion highlights the need to understand the relationship between mass flow rate and velocity of the air being ejected. The correct approach involves calculating the momentum change to determine the thrust produced by the engine. Understanding these principles is essential for accurately solving jet engine thrust problems.
chrishere?
Messages
1
Reaction score
0

Homework Statement


A jet engine gets it thrust by taking in air, heating and compressing it, and then ejecting it at a high speed. IF a particular engine takes in 20 k/g of air per second at 100 m/s and ejects it at 500 m/s calculate the thrust of the engine.
chriss #getmoney: thrust of the engine would be v right?

Homework Equations



i believe that the equation is Mv1 + Mv2 = V(Mv1+Mv2) and that the thrust = V .



The Attempt at a Solution

 
Physics news on Phys.org
Thrust is a force rather than velocity.

Hint: Try using Newton's Second Law.

Edit: The equation that you have written doesn't make sense, it simplifies to V=1 for all M and v.
 
Last edited:
Welcome to PF!

chrishere? said:
A jet engine gets it thrust by taking in air, heating and compressing it, and then ejecting it at a high speed. IF a particular engine takes in 20 k/g of air per second at 100 m/s and ejects it at 500 m/s calculate the thrust of the engine.
chriss #getmoney: thrust of the engine would be v right?
…
i believe that the equation is Mv1 + Mv2 = V(Mv1+Mv2) and that the thrust = V .

Hi chrishere?! Welcome to PF! :smile:

Thrust is a force, so use Newton's second law in the form force = rate of change of momentum.

How much momentum is being ejected? :wink:
 

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'Collision of a bullet on a rod-string system: query'

Thread 'Collision of a bullet on a rod-string system: query'

In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
View full post »

Similar threads

Why is the thrust equation same under gravitational force?
Replies
10
Views
2K
Newton's Laws Conceptual Problem
Replies
2
Views
9K
Rocket acceleration problem: confused about Newton's 2nd Law
Replies
42
Views
5K
Jet Engine Question Homework: Find Thrust w/ 100% Efficiency
Replies
1
Views
2K
Force and acceleration of a rocket
Replies
3
Views
2K
Forces - Space Shuttle Takeoff Calculations
Replies
22
Views
2K
Rocket Thrust, Acceleration, Velocity and Altitude
Replies
16
Views
8K
How do I Calculate Average Thrust when given t, v, delta m
Replies
3
Views
2K
Newton's Second Law Rocket Problem
Replies
13
Views
2K
How Is Thrust Calculated for a Jet Engine in a Lab Test?
Replies
7
Views
4K

Hot Threads

Recent Insights

Back
Top