Calculating torque about a point with given forces

AI Thread Summary
The discussion revolves around calculating torque at point A using given forces and angles. The initial calculation yielded a torque of -274.808 Nm, which differs from the textbook answer of -295 Nm, leading to confusion about potential errors. Participants noted that finding angles was unnecessary, suggesting simpler methods using right triangle ratios. One user pointed out that a missing force or weight might explain the discrepancy in the expected answer. The conversation emphasizes the importance of verifying calculations and considering all forces involved in torque problems.
Nova_Chr0n0
Messages
16
Reaction score
3
Homework Statement
What is the net torque around point A?
Relevant Equations
τ = rF
wew1.JPG

I've inserted a photo of the figure, hope everyone can see it.

SOLUTION:
1. I first solved for the angle of 100 N and 50 N since I need the force that is perpendicular to point A.
>> Angle of 100 N
theta = arctan(3/4)
theta = 36.870 degree
>> Angle of 50 N
theta = arctan(12/5)
theta = 67.380 degree
2. Solving for the net torque on point A where counter-clockwise is + and clockwise is -
τ = rF
τ_A = -1[100sin(36.870)] - 1.75(70) - 2[50sin(67.380)]
τ_A = -274.808 Nm

My final answer for the torque at point A is -274.808 Nm, but when I check the answer in the textbook, it is -295 Nm. I am confused about what part I did wrong. Also, I'm new to the forum, so if my format is not understandable, kindly inform me about it. Thanks!
 
Physics news on Phys.org
Finding the angles was rather unnecessary since you are given the right triangle ratios. You could just write 100N x 1m x (3/5) etc.
But I get the same answer as you do.
 
  • Like
Likes Nova_Chr0n0
Well, I've got 274.8 as well, though my solution is somewhat less convolute than yours.

Is there anything else to the question ?
 
  • Like
Likes Nova_Chr0n0
haruspex said:
Finding the angles was rather unnecessary since you are given the right triangle ratios. You could just write 100N x 1m x (3/5) etc.
But I get the same answer as you do.
I guess there was just an error in the given answer for the file that I've encountered. Also, thanks for letting me know a solution with less work when involving triangle ratios. Really appreciate it!
 
Nova_Chr0n0 said:
I guess there was just an error in the given answer for the file that I've encountered. Also, thanks for letting me know a solution with less work when involving triangle ratios. Really appreciate it!
Welcome, @Nova_Chr0n0 !

That dimension of 1 m to the right of the figure suggests that either a force that is applied at the right end, or the weight of the 3-meter bar, is missing.
 
  • Informative
Likes Nova_Chr0n0
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 .
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...
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