Problem statements
Solution video - H17.A
Solution video - H17.B
DISCUSSION THREAD
Please post questions here on the homework, and take time to answer questions posted by others. You can learn both ways.
HOMEWORK 17 - SP 25
19 thoughts on “HOMEWORK 17 - SP 25”
Leave a Reply
You must be logged in to post a comment.
I found that the homework 15 problem made a good reference for identifying how to set up the tension forces on the blocks. The example problem from the general force lecture was also helpful when setting up the equilibrium force equations.
Regarding the tension between D and C would it be 2T cause there is two cords or 1T ?
There seems to be two cord of equal magnitude on D, so 2T would seem appropriate to get the tension of 1 cable.
I believe you are correct. The tension throughout the cable should be equal, so when it wraps around looking like "2 cords", we effectively have 2T acting on block B.
I think 2T.
It should be 2T because there are two ropes
I assumed that the acceleration of the two blocks were equal in order to solve this question. Would this be a valid assumption even though they are connected by a two pully system?
The system is in equilibrium, so you shouldn't have to worry about acceleration. To your point though, because of the way the pulleys are arranged the tension forces on the blocks aren't equal.
The system is in equilibrium; therefore, acceleration is 0. This is a pretty straightforward problem. You have to find the net force equation for both boxes and then add them together. Make sure to get rid of T during the calculation.
I thought that drawing free body diagrams for blocks A and B was helpful for me to solve this problem. It helped me visualize all of the forces acting on each of the blocks. Therefore, I could go back and ensure that my equations for blocks A and B were accurate.
The key to this one for me was noticing the tension relationships between the left and right side of the pulley. With that information it simplified down and made the friction quite simple to find with the two equations from the two FBDs.
One confusing thing for me is the relationship between the tension in the string and the force the tension exerts on the objects. If the tension in the string is T, then would block B experience a force of 2T?
Yes block B would experience a force of 2T because if you take only the FBD for block B there are two strings pulling it each with tension T.
It's been a while since I've worked with slopes. For the forces on the block on the slope, you use the direction of the surface as the direction of the x axis, correct? That way you can find the normal force from the surface = the "vertical" component of the weight?
Yes, I believe the surface is considered the x-axis and you can use that to find the normal force
Is Block A experience a tension of T and block B with 2T?
Are the tensions on both sides equal?
The tension in the rope is constant, as it appears to be the same rope throughout. However, the force of tension on block B is going to be 2T since there are "two" ropes pulling on it.
Based on the diagram, it can be seen that block B is experiencing twice the tension of block A due to the cable wrapping around the pulley. I solved this problem by breaking it up into a system for each block. I solved for the equivalent tension of each block and set them equal to each other. Doing so yields an equation in terms of the coefficient of friction required.