- #1

LuigiAM

- 55

- 7

Hi everyone,

This is not really a homework question per se since it's not an assignment. Basically, our physics professor gave us a 100+ page syllabus filled with example questions and solutions and I am practicing with them by doing them one after the other. This one question I'm having trouble with. Here it is:

The first thing that pops into my mind is that the rod is 1 meter long, and according to the professor's solution point P must be 1.25 meters from the end of the rod. However, in the drawing, the point P is actually on the rod. It seems a bit unintuitive to me that the force would be acting outside of the rod?

For the position of the resultant, my calculations are like this if x is the distance between points P and O:

(10 kg)(x) - (15 kg)(0.5 - x) - (5 kg)(1 - x) = 0

(10 kg)(x) - 7.5 kg + (15 kg)(x) - (5 kg) + (5 kg)(x) = 0

x (10 kg + 15 kg + 5 kg) = 7.5 kg + 5 kg

x (30 kg) = 12.5 kg

x = 12.5 kg / 30 kg = 0.42

I'm not sure what I'm doing wrong? I think the solution has all the forces as a negative when he's adding them up, but shouldn't the 10 kg force be a different sign than the 15 kg and the 5 kg one?

Thanks for any help

(Note: I ticked the box saying that I used the template, but I don't think it applies for this question since it's not really an assignment, it's just a question with the solution and I need help understanding the solution. I hope it's ok)

This is not really a homework question per se since it's not an assignment. Basically, our physics professor gave us a 100+ page syllabus filled with example questions and solutions and I am practicing with them by doing them one after the other. This one question I'm having trouble with. Here it is:

The first thing that pops into my mind is that the rod is 1 meter long, and according to the professor's solution point P must be 1.25 meters from the end of the rod. However, in the drawing, the point P is actually on the rod. It seems a bit unintuitive to me that the force would be acting outside of the rod?

For the position of the resultant, my calculations are like this if x is the distance between points P and O:

(10 kg)(x) - (15 kg)(0.5 - x) - (5 kg)(1 - x) = 0

(10 kg)(x) - 7.5 kg + (15 kg)(x) - (5 kg) + (5 kg)(x) = 0

x (10 kg + 15 kg + 5 kg) = 7.5 kg + 5 kg

x (30 kg) = 12.5 kg

x = 12.5 kg / 30 kg = 0.42

I'm not sure what I'm doing wrong? I think the solution has all the forces as a negative when he's adding them up, but shouldn't the 10 kg force be a different sign than the 15 kg and the 5 kg one?

Thanks for any help

(Note: I ticked the box saying that I used the template, but I don't think it applies for this question since it's not really an assignment, it's just a question with the solution and I need help understanding the solution. I hope it's ok)