Two-Block Dynamics Problem: Determining Acceleration and Tension

In summary, the problem involves determining the acceleration of two blocks and the tension in two cords, given that there is no friction and the pulleys and rope have negligible mass. Using the equations ΣF = ma and T1 = 2T2, with block A weighing 100kg and block B weighing 300kg, a solution can be found by assuming a relationship between the x and y accelerations. The correct solution is ax = 8.4m/s^2 and ay = 4.2m/s^2.
  • #1
whitejac
169
0

Homework Statement


Assuming no friction is on the plane or the pulleys and the pulley and rope have negligible mass... Determine the acceleration of each block and the tension in each cord. Block A weighs 100kg, Block B weighs 300kg.
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Homework Equations


ΣF = ma
ma = 100kg
mb = 300kg

The Attempt at a Solution



ΣFx = max = T1 = 100ax
ΣFy = may = W - T2 = 2943kg - T2 = 300ay
T1=2T2

I know that I have the relationships right, but I don't know exactly how to extract them...
 
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  • #2
What is the relationship between ax and ay? It is constrained motion, so you relate the two accelerations.
 
  • #3
I think I solved it this way based off of what my professor drew on the board but I need some clarity because I'm not quite sure how this can be...
if we assume:

ax = 2ay
^My professor's hint

then we have 4 relations and 4 unknowns. So:

T1 = 2T2
100ax = 2[2943 - 300ay]
50ax = 2943 - 300ay
ax = 2ay
50*2ay = 2943 - 300ay
400ay = 2943

ay = 7.3m/s^2
ax = 14.8 m/s^2

**Edit**
This is an incorrect answer. The correct answer is 8.4m/s^2 for ax which means somewhere my answer is almost 2 times larger.
 
Last edited:

Related to Two-Block Dynamics Problem: Determining Acceleration and Tension

1. What is the "2 block problem" in dynamics?

The "2 block problem" in dynamics refers to a common scenario in which two blocks are connected by a string and are subject to external forces. The goal is to determine the resulting motion of the two blocks.

2. How do you approach solving a 2 block problem in dynamics?

The first step in solving a 2 block problem is to draw a free-body diagram for each block, identifying all the forces acting on them. Then, using Newton's laws of motion and the equation F=ma, you can set up and solve equations to determine the acceleration and motion of the blocks.

3. What are some common assumptions made when solving a 2 block problem?

Some common assumptions made when solving a 2 block problem include assuming the string connecting the blocks is massless and inextensible, neglecting friction, and assuming the blocks are point masses with all their mass concentrated at a single point.

4. How do you account for the effects of friction in a 2 block problem?

If friction is not neglected in a 2 block problem, it can be accounted for by adding the frictional force (Ff) to the free-body diagram and including it in the equations of motion. The value of Ff can be calculated using the coefficient of friction and the normal force.

5. Can a 2 block problem have more than one solution?

Yes, a 2 block problem can have more than one solution. This can occur when the external forces on the blocks are balanced, resulting in multiple possible combinations of acceleration and motion for the blocks. In this case, additional information or constraints are needed to determine the unique solution.

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