Quick question about resultant forces of tugboats

In summary, the conversation discusses the process of finding the angle between the force vectors and the x-axis in a scenario where a ship is being pulled by tugboats with forces of 300 N and 800 N at a 45 degree angle. The question of whether the angle would be 22.5 degrees or different due to the different magnitudes of the forces is raised, and it is determined that the x-axis should be defined in order to solve the problem. The conversation also explores different methods of defining the x-axis and calculating the magnitude, with the conclusion that the x-axis should be defined as "pointing along the 800N force" for accurate results.
  • #1
TomRiddle
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0
Member advised to use the homework template for posts in the homework sections of PF.
A ship is being pulled by tugboats with forces of 300 N and 800 N. The angle between the forces is 45 degrees.

My question is how can we find the angle between the force vectors and the x-axis? Would it just be 45/2 =22.5 degrees or would it be different because the forces have different magnitudes?

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  • #2
The two forces are 45deg to each other? No "x-axis" has been defined so you need to work out if you are free to pick any axis system you like.
The answer seems to suggest not... therefore: not enough information.
 
  • #3
I would assume the x-axis to be the direction the tugboat is moving in. Or at least perpendicular to the left side of the rectangle representing the tugboat. Are you saying this problem is unsolvable?

I tried defining the x-axis as bisecting the 45 degree angle:
300cos157.5 + 800cos202.5 = -1016.27
300sin157.5 + 800sin202.5 = -191.34
arctan(191.34/1016.27) = 10.66 (rounding to 11 this does give me the 191 degree angle, matching the given answer)

But, the magnitude = sqrt(1016.27^2 + 191.34^2) = 1034.13 which is different from the provided answer
 
  • #4
TomRiddle said:
I would assume the x-axis to be the direction the tugboat is moving in. Or at least perpendicular to the left side of the rectangle representing the tugboat.
How would you justify these assumptions?
Note: you are not told which direction the tugboat is moving in when the forces are applied - from the forces you can figure out which direction the acceleration is in, but only with respect to one of the forces. You are only told the direction of the forces wrt each other, not to anything else - like you are not told their direction wrt the front of the block representing the ship they are towing.

Are you saying this problem is unsolvable?
You have to define a coordinate system - you should be able to do that without using the provided answer.
The first step in your working has to state this definition ... ie. I would be inclined to add the vectors head-to-tail (sketch) and use the cosine and sine rules, being careful to label everything.

I tried defining the x-axis as bisecting the 45 degree angle:
300cos157.5 + 800cos202.5 = -1016.27
300sin157.5 + 800sin202.5 = -191.34
arctan(191.34/1016.27) = 10.66 (rounding to 11 this does give me the 191 degree angle, matching the given answer)
... yeah, it looks like the x-axis for the model answer is defined to be in the opposite direction to the initial orientation of the ship (assuming the tug boats are pulling from the bow) ie the +x direction is from bow to stern along the ship axis. But there is no reason to do this except maybe the convention that x is "to the right on the page". That is nonsense... but useful to remember if you have this same person set an exam in future.

But, the magnitude = sqrt(1016.27^2 + 191.34^2) = 1034.13 which is different from the provided answer
Try the head-to-tail approach w cosine rule, or define the x-axis as "pointing along the 800N force", to check your magnatude.
 

Related to Quick question about resultant forces of tugboats

What is a resultant force?

A resultant force is the overall force acting on an object, taking into account all the individual forces acting on it.

How do you calculate the resultant force?

To calculate the resultant force, you need to add up all the individual forces acting on an object. This can be done by using vector addition, where you consider the magnitude and direction of each force.

What are the factors that affect the resultant force of a tugboat?

The resultant force of a tugboat is affected by factors such as the engine power, the maneuverability of the tugboat, the weight of the towed object, and external forces like wind and current.

Can the resultant force of a tugboat change during towing?

Yes, the resultant force of a tugboat can change during towing. This can happen due to changes in the direction or speed of the tugboat, or if external forces such as wind or current change.

Why is understanding the resultant force important in tugboat operations?

Understanding the resultant force is important in tugboat operations because it helps in determining the necessary power and maneuvering strategies for safe and efficient towing. It also helps in predicting the behavior of the tugboat and the towed object in different conditions.

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