Upward velocity of a block on a string

AI Thread Summary
The discussion focuses on calculating the upward velocity of a block suspended from a spring after being pulled down and released. The spring has a force constant of 600 N/m and is initially stretched to 0.86m before being released. The conservation of energy principle is applied, with initial and final kinetic and potential energy equations set up. There is a debate about whether gravitational potential energy should be considered negative, depending on the reference point chosen. The final upward velocity calculated is 1.92 m/s, but adjustments for gravitational potential energy are necessary for accuracy.
ethex
Messages
25
Reaction score
0

Homework Statement


The force constant of a spring is 600 N/m and the un-stretched length is 0.72m. A 3.2kg block is suspended from the spring. An external force slowly pulls the block down, until the spring has been stretched to a length of 0.86m. The external force is then removed, and the block rises. In this situation, when the spring has the contracted to a length of 0.72m, What is the upward velocity of the block?

Homework Equations


conservation of energy

The Attempt at a Solution



KEinitial + Uinitial = KEfinal + Ufinal
0 + 0.5(600)(0.14)^2 = 0.5 x 3.2 x v^2 + 0
v = 1.92m/s?
 
Physics news on Phys.org
Don't forget that gravity is working on the block too!
 
KEinitial + Uinitial = KEfinal + Ufinal
0 + 0.5(600)(0.14)^2 + (3.2)(9.8)(0.14) = 0.5 x 3.2 x v^2 + 0

Is this right?
 
ethex said:
KEinitial + Uinitial = KEfinal + Ufinal
0 + 0.5(600)(0.14)^2 + (3.2)(9.8)(0.14) = 0.5 x 3.2 x v^2 + 0

Is this right?

Better, but should the gravitational PE be negative? (It looks like you're taking the zero reference for it at the unstretched spring level).
 
Thank you, that is what i am missing out.
 

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

How Does Gravity Affect the Velocity of a Block on a Spring?
Replies
6
Views
2K
Final velocity of two blocks between a spring
Replies
2
Views
3K
How Do Friction and Spring Constants Affect Block Velocities?
Replies
16
Views
3K
First post: work and energy problem
Replies
5
Views
2K
Kleppner - blocks and a compressed spring
Replies
3
Views
3K
Kinetics: Two Blocks and a Spring
Replies
9
Views
2K
Oscillating Spring Block System inside elevator
Replies
8
Views
5K
Equation of motion for the system, and determine the frequen
Replies
8
Views
1K
How many oscillations until a damped block comes to rest?
Replies
6
Views
2K
Block on a spring on a horizontal surface with friction?
Replies
9
Views
3K

Hot Threads

Recent Insights

Back
Top