Register to reply

Blocks connected by rope, Newton's Third Law

by StephenDoty
Tags: blocks, connected, newton, rope
Share this thread:
StephenDoty
#1
Mar14-08, 08:10 AM
P: 267
The figure shows two 1.0 kg blocks connected by a rope. A second rope hangs beneath the lower block. Both ropes have a mass of 250 g. The entire assembly is accelerated upward at by force. What is F? What is the tension at the top end of rope 1? What is the tension at the bottom end of rope 1? What is the tension at the top end of rope 2?


The force on block B:
T-(m of B)g=(m of B)a

The force on block A:
F-[(m of a + m of b)g] = (m of b)a

What do I do now?
Thank you.
Stephen
Attached Thumbnails
knight_Figure_08_26.jpg  
Phys.Org News Partner Science news on Phys.org
New type of solar concentrator desn't block the view
Researchers demonstrate ultra low-field nuclear magnetic resonance using Earth's magnetic field
Asian inventions dominate energy storage systems
Doc Al
#2
Mar14-08, 08:20 AM
Mentor
Doc Al's Avatar
P: 41,429
To find F, consider the masses and ropes as a single system. What external forces act on the system? What's the acceleration?
StephenDoty
#3
Mar14-08, 11:03 AM
P: 267
The figure shows two 1.0 kg blocks connected by a rope. A second rope hangs beneath the lower block. Both ropes have a mass of 250 g. The entire assembly is accelerated upward at by force. What is F? What is the tension at the top end of rope 1? What is the tension at the bottom end of rope 1? What is the tension at the top end of rope 2?


If we make it one system the external forces are: F and weight of the blocks
So F= (m of a + m of b + 2*m of rope)a
and w=(m of a + m of b + 2*m of rope)g

since F-w=(m of a + m of b +2*m of rope)a, right??
Now what??

Thank you.

Doc Al
#4
Mar14-08, 11:26 AM
Mentor
Doc Al's Avatar
P: 41,429
Blocks connected by rope, Newton's Third Law

Quote Quote by StephenDoty View Post
If we make it one system the external forces are: F and weight of the blocks
Right.
So F= (m of a + m of b + 2*m of rope)a
No. (The net force will equal M*a, but that comes later.)
and w=(m of a + m of b + 2*m of rope)g
Right.
since F-w=(m of a + m of b +2*m of rope)a, right??
Right!
Now what??
What's the acceleration? That must be given. Use it to solve for F.


Register to reply

Related Discussions
Two blocks with different mass are attached to either end of a light rope that passes Introductory Physics Homework 8
Finding Tension in Rope connected to rod Engineering, Comp Sci, & Technology Homework 2
Two Blocks, Massless Rope. Pulley Introductory Physics Homework 1
Connected Blocks HeLP Introductory Physics Homework 3
2 blocks connected by a metal pull on an inclined plane Introductory Physics Homework 2