Getting wrong answer in an (angular) impulse momentum problem

AI Thread Summary
The discussion centers on resolving an impulse momentum problem in an angular context, where the initial answer of 12mu/(3+cos2α) was consistently obtained. The participant struggled with their approach, which involved treating the rod arrangement as rigid, but was advised to consider it with a free joint instead. This adjustment led to the correct solution. The participant acknowledged their oversight regarding forum rules and expressed gratitude for the assistance received. The conversation highlights the importance of correctly interpreting physical arrangements in problem-solving.
Divya
Messages
9
Reaction score
1
Homework Statement
Three masses m, 2m and 3m are connected by two massless and rigid rods
of length l which are currently perpendicular to each other, as shown in the
figure. If the masses initially travel at velocity u towards a vertical wall and
mass m undergoes a collision with the wall, determine the impulse delivered
by the wall to mass m if the final horizontal velocity of mass m is zero. There
is no friction between the wall and mass m. Assume that the tensions in the
rods are strictly longitudinal (because they are massless).
Relevant Equations
impulse = change in momentum
angular impulse = change in angular momentum
1660974019799.png


WhatsApp Image 2022-08-20 at 11.18.12 AM.jpeg

I have tried this same approach three times and I got the same answer. I can't figure out what's wrong. Btw answer is 12mu/(3+cos2α)
And yes, sorry for my shitty handwriting. If you can't understand the reasoning behind any step then please let me know.
 
Physics news on Phys.org
Divya said:
sorry for my shitty handwriting
Forum rules state that images are for diagrams and textbook extracts. Please type in your working, preferably in LaTeX.
Also, it helps if you provide some explanation of your approach and define all variables.

It looks to me as though you are taking the rod arrangement as rigid. It only says initially a right angle. I would take it as having a free joint.

In my experience, it rarely gains anything to bother finding the mass centre of such an assemblage anyway.
 
I am really sorry for not seeing the rules of forum before posting ( I am new here). Also thanks for your help. The 'free joint' interpretation gave the right answer.
 
Divya said:
I am really sorry for not seeing the rules of forum before posting ( I am new here). Also thanks for your help. The 'free joint' interpretation gave the right answer.
well done
 

Thread 'Rolling without slipping on a curved surface'

Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
View full post »
Thread 'Trying to understand the logic behind adding vectors with an angle between them'

Thread 'Trying to understand the logic behind adding vectors with an angle between them'

My initial calculation was to subtract V1 from V2 to show that from the perspective of the second aircraft the first one is -300km/h. So i checked with ChatGPT and it said I cant just subtract them because I have an angle between them. So I dont understand the reasoning of it. Like why should a velocity be dependent on an angle? I was thinking about how it would look like if the planes where parallel to each other, and then how it look like if one is turning away and I dont see it. Since...
View full post »
Thread 'Correct statement about a reservoir with an outlet pipe'

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...
View full post »

Similar threads

Problem in understanding angular momentum of a rigid body
Replies
10
Views
2K
Analyzing an Angular Impulse Problem
Replies
12
Views
2K
Application of angular impulse to a problem
Replies
7
Views
2K
Why did I get this angular momentum problem wrong?
Replies
25
Views
11K
Describing the translation and rotation of a square frame
Replies
3
Views
2K
Elastic collision of particle and rotating disc
Replies
7
Views
2K
Linear and angular momentum problem: Ball hitting a rod
2
Replies
62
Views
13K
Solving Toppling Hemisphere Problem with Momentum & Angular Momentum
Replies
19
Views
3K
Conservation of Linear Momentum of Rigid Body
Replies
3
Views
1K
Problem About Change in Momentum/Impulse
Replies
8
Views
2K

Hot Threads

Recent Insights

Back
Top