Work done on an Object - Pulling a wagon while lifting up at an angle

AI Thread Summary
Juri is pulling a wagon with a force of 200 Newtons at a 35-degree angle over a distance of five kilometers. An initial calculation using the formula W = F*d*cos(theta) resulted in 819.2 kJ, but the provided solution incorrectly used W = F*d*sin(theta), yielding 573.6 kJ. The discussion centers on why the cosine function is appropriate for calculating work in this scenario, as it accounts for the horizontal component of the force. Participants agree that the cosine function should be used, highlighting the error in the official solution. The conversation emphasizes the importance of accuracy in both calculations and significant figures.
jigsaw21
Messages
20
Reaction score
0
Homework Statement
This question is asking to find the work done on an object being pulled at an angle.
Relevant Equations
W = F*d*cos theta
Juri is tugging her wagon behind her on the way to... wherever her wagon needs to go. The wagon repair shop. She has a trek ahead of her--five kilometers--and she's pulling with a force of 200 Newtons. If she's pulling at an angle of 35 degrees to the horizontal, what work will be exerted on the wagon to get to the repair shop?

...

Attempted Solution: I simply plugged in the values given into the formula above for Work which is F*d*cos (theta) due to the question saying that she was pulling at an angle of 35 degrees to the horizontal. This gave me an answer of 819.2 kJ. However, in the solution it is saying the appropriate formula should be W = F*d*sin (theta) instead of cos (theta), and thus the solution is 573.6 kJ.

But my question is why is sin(theta) used instead of cos(theta) for the formula . I thought that if the direction the wagon is being pulled needs to be parallel to the horizontal component of the Force, which should be cos (theta)?

I'm just curious if anyone could help me see why W = F*d*sin(theta) is the appropriate formula for this example and not W = F*d*cos(theta).

I appreciate any response or feedback.
 
Last edited by a moderator:
Physics news on Phys.org
jigsaw21 said:
Homework Statement:: This question is asking to find the work done on an object being pulled at an angle.
Relevant Equations:: W = F*d*cos theta

Juri is tugging her wagon behind her on the way to... wherever her wagon needs to go. The wagon repair shop. She has a trek ahead of her--five kilometers--and she's pulling with a force of 200 Newtons. If she's pulling at an angle of 35 degrees to the horizontal, what work will be exerted on the wagon to get to the repair shop?

...

Attempted Solution: I simply plugged in the values given into the formula above for Work which is F*d*cos (theta) due to the question saying that she was pulling at an angle of 35 degrees to the horizontal. This gave me an answer of 819.2 kJ. However, in the solution it is saying the appropriate formula should be W = F*d*sin (theta) instead of cos (theta), and thus the solution is 573.6 kJ.

But my question is why is sin(theta) used instead of cos(theta) for the formula . I thought that if the direction the wagon is being pulled needs to be parallel to the horizontal component of the Force, which should be cos (theta)?

I'm just curious if anyone could help me see why W = F*d*sin(theta) is the appropriate formula for this example and not W = F*d*cos(theta).

I appreciate any response or feedback.
It's a mistake, You are correct. Cos(35º) should be used.

Also, note the data are given to only 1 or 2 significant figures. I'd round the answer to 2 significant figures.

The fact that the 'official' solution is both wrong and given to 4 significant figures isn't inspiring!
 
Thread 'Collision of a bullet on a rod-string system: query'
In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
Back
Top