Calculating Acceleration and Tension in a Simple Force Question | Homework Help

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In summary, the ice will hit the bottom in 2 seconds, at an angle of 45 degrees, and with an acceleration of 2g.
  • #1
oreosama
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Homework Statement



a load of bricks of mass m hangs from one end of a rope that passes over a small frictionless pulley. a counterweight, twice as heavy, is suspended from the other end of the rope. given m determine the accel of the masses and the tension in the rope

Homework Equations


f=ma


The Attempt at a Solution



Fa=-2mg + T

2m*a=-2mg + T

a= (-2mg+T)/2m

plug in accel in other force

Fb = -mg + T

m((-2mg+T)/2m) = -mg + T

-2mg + T = -2mg + 2T

T = 2T

T=0?


i have no idea if I am doing anything remotely close to the right path, if I'm way off please explain like a baby as I'm confused thanks for help
 
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  • #2
Fa=-2mg + T

2m*a=-2mg + T

a= (-2mg+T)/2m

plug in accel in other force

Fb = -mg + T

m((-2mg+T)/2m) = -mg + T

-2mg + T = -2mg + 2T
----------------------------
FFrom your calculation for Fa, T is greater than 2mg, so it is going up.
When one side going up, the other side should be going down.

But for calculation for Fb, T is greater than mg. It means going up, where you have assumed that it should be going down.
It is a single cable.
 
  • #3
m(a-g)+T= 2mg-T
ma= 3mg-2T
a=(3g-2(T/m))

this is the acceleration of the mass?
 
  • #4
You would understand the problem better with a drawing showing the forces on both objects, brick and counterweight, as in the attachment.

In what direction will the brick and counterweight move? What is the net force acting on the brick? What is the net force acting on the counterweight?
How are the accelerations related?

ehild
 

Attachments

  • brickpulley.JPG
    brickpulley.JPG
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  • #5
so since pulley requires each to go in opposite direction you make one force negative relative to coordinate system:

(using fa from above)

fb = -mg + T
-ma = -mg + T

...

T = 4/3mg?
 
  • #6
T=4/3 mg is correct.

ehild
 
  • #7
I don't want to open another thread
A block of ice of mass m is released from rest at the top of a frictionless ramp of length L. at the bottom of the incline the speed of the ice is v1. given m,L,v1 determine

the time needed to hit the bottom
the angle between the ramp and the horizontal
the accel of the ice

I made my coordinate system slant at the angle of the ramp because I thought this would make it less work

http://i.imgur.com/d18GN.png

(is this okay?)
x0 = 0
x = L
v0 = 0
v = v1
a= A
t = T

v1 = 0 + AT

T = v1/A

v1^2 = 2AL

A = v1^2 / 2L

T = v1 / (v1^2 / 2L)

T = 2L / v1

I got these answers pretty cleanly but I have no idea what I should be doing to get theta since I don't see a way to get the lengths of the potential triangle with hypoteneus L
 
  • #8
a=gSinθ
 

What is a simple force?

A simple force is a push or pull on an object that results in a change in the object's motion or shape. It is a fundamental concept in physics and can be represented by a vector with magnitude and direction.

What is the difference between a simple force and a complex force?

A simple force acts on a single object and has a single direction and magnitude. A complex force, on the other hand, is the combination of multiple simple forces acting on an object.

What are some examples of simple forces?

Some examples of simple forces include gravity, friction, tension, and normal force. These forces can be either contact forces (such as pushing or pulling an object) or non-contact forces (such as the force of gravity).

How is a simple force calculated?

The magnitude of a simple force can be calculated using the equation F = m x a, where F is the force, m is the mass of the object, and a is the acceleration. The direction of the force is determined by the direction of the acceleration.

How can simple forces be used in everyday life?

Simple forces play a crucial role in our daily lives. For example, the force of gravity keeps us on the ground, and friction allows us to walk without slipping. We also use simple forces when we push or pull objects, such as opening a door or pushing a shopping cart. In addition, simple forces are essential in engineering and design, as they help determine the stability and strength of structures and machines.

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