About force and motion in Physics

[Johnny Leong]

Question: Team A and B are competing in a tug-of-war. Team A is winning. Assuming that the mass of the rope is negligible, which of the following statements are correct. Explain your answer.
i. The force exerted by A on B is greater than the force exerted by B on A.
Ans. I think this is right. Because A is winning.
ii. The frictional force exerted by A on the ground is greater than that exerted by B on the ground.
Ans. I think this is not correct. Because not A exerts friction on the ground, the direction should be reversed.
iii. The frictional force exerted by the ground on A is greater than that exerted by the ground on B.
Ans. I think this is correct. Because A exerts more force, the friction exerts on A is also greater.

The rope will break if the force exerted on it is greater than 5000 N. Will the rope break in the tug-of-war if two teams pull on it, each with a force of 3000 N?
Ans. I think the rope will not break. Because the force of each team is still below 5000 N, even they exert 3000 N but they are in different directions. The main point is that the resultant force acted on the rope is still below 5000 N.

Please tell me if my answer is right or not. Thank you for reading.

 

[HallsofIvy]

Question: Team A and B are competing in a tug-of-war. Team A is winning. Assuming that the mass of the rope is negligible, which of the following statements are correct. Explain your answer.

i. The force exerted by A on B is greater than the force exerted by B Question: Team A and B are competing in a tug-of-war. Team A is winning. Assuming that the mass of the rope is negligible, which of the following statements are correct. Explain your answer.
i. The force exerted by A on B is greater than the force exerted by B on A.
Ans. I think this is right. Because A is winning.

No, the force exerted by A on B is exactly the same a the force exerted by B on A. (Equal and opposite reaction)

ii. The frictional force exerted by A on the ground is greater than that exerted by B on the ground.
Ans. I think this is not correct. Because not A exerts friction on the ground, the direction should be reversed.

Why would you think A is not exerting friction on the ground? Suppose A were a bunch of enormous strong men who were sitting on ice and the other end of the rope were attached to a tree. The tree doesn't pull at all, the men pull with great force. Who moves towards whom?

iii. The frictional force exerted by the ground on A is greater than that exerted by the ground on B.
Ans. I think this is correct. Because A exerts more force, the friction exerts on A is also greater.

You got this one right! But your reason makes no sense. The friction the ground exerts on A is exactly the same as the friction A exerts on the ground!

The rope will break if the force exerted on it is greater than 5000 N. Will the rope break in the tug-of-war if two teams pull on it, each with a force of 3000 N?
Ans. I think the rope will not break. Because the force of each team is still below 5000 N, even they exert 3000 N but they are in different directions. The main point is that the resultant force acted on the rope is still below 5000 N.

Once again, correct answer, bad reason. If both teams were exerting 3000N in the SAME direction, there would be no tension in the rope- it would go flying very fast in that direction but there would be no tension! The reason the rope won't break is this: suppose one team were exerting 3000 N force on the rope and the rope were tied to a tree. There would be 3000N tension in the rope (so it doesn't break) but the fact that the rope doesn't move means that the tree is exerting 3000 N force on the rope also. This is exactly the situation you have in the problem. One team is exerting 3000 N force on the rope. The fact that the other team is also exerting 3000 N on it just tells us that the rope is not moving in one or the other direction. The tension in the rope is still 3000 N- less than 5000.

 

[M98Ranger]

Your response to the first question is correct. Team A is winning because they are exerting a greater force on the rope than Team B.

For the second question, you are correct that the frictional force exerted by A on the ground is not greater than that exerted by B on the ground. Both teams are exerting the same force on the ground, but in opposite directions. Friction always acts in the opposite direction of motion, so the direction of the frictional force will be reversed for each team.

For the third question, your answer is correct. The frictional force exerted by the ground on A will be greater than that exerted on B because A is exerting a greater force on the ground.

In regards to the last question, you are correct that the rope will not break if both teams are pulling with a force of 3000 N each. This is because the resultant force on the rope will be 0 N, since the forces are equal and opposite. The rope will only break if the resultant force exceeds the maximum limit of 5000 N.