Hello, and thanks!kuruman said:Hi berrytea and welcome to PF>
It would help if you showed us what exactly you did under "The attempt at a solution". It would also be more useful if you formulated a strategy instead of looking for a formula. How do you think yo should proceed to find the change in mechanical energy? You have a "Relevant equation". That's a good beginning. What must you do to implement it?
Never mind your friend. We are interested in what you did and what it means. First of all what is the system for which you want to calculate the change in mechanical energy? Is it just the block or the block and ball together?berrytea said:Hello, and thanks!
My attempt was to find the change in kinetic and potential energies and add them. What is confusing to me, is a friend of mine got -52 J for this solution. I calculated ΔPE = -30.25 J and I got simply ΔE = 30 J, which gives me -0.25 as ΔKE. So I am not sure what I'm doing wrong or which answer is correct.
I am unsure, but I assume it is the block and the ball together as the question does not specify.kuruman said:Never mind your friend. We are interested in what you did and what it means. First of all what is the system for which you want to calculate the change in mechanical energy? Is it just the block or the block and ball together?
Do you mean the stone comes from the right or moves to the right?berrytea said:It is struck by a 3.00 kg stone at 8.00 m/s to the right, then rebounds at 2.00 m/s to the left.
Ball? Stone?berrytea said:I assume it is the block and the ball together
I would say it is the block andberrytea said:I am unsure, but I assume it is the block and the ball together as the question does not specify.
The stone is traveling to the right and it (the stone) rebounds at 2.00 m/s to the left.haruspex said:Do you mean the stone comes from the right or moves to the right?
What rebounds at 2m/s? Do you mean the block moves off left at 2m/s, or the stone rebounds from the collision at 2m/s?
Where does the spring come into this? Is the rebound immediate or after some spring compression and expansion? Or are there more parts to the question?
I think ΔU = 30.35 Jkuruman said:I would say it is the block andballstone together. First things first. What do you think ΔU is in this case?
Can you explain what are the two points between which you are asked to calculate the change in mechanical energy? Is it from the start of the collision to when the spring is fully compressed?berrytea said:I think ΔU = 30.35 J
Yes, it is during the collision, so from the start to the end when the spring is fully compressed.kuruman said:Can you explain what are the two points between which you are asked to calculate the change in mechanical energy? Is it from the start of the collision to when the spring is fully compressed?
At maximum compression the blocks are moving together with speed V which you have not found yet. Then ΔK=½(m1+m2)V2-½m1v12 where v1 = initial speed of the stone.berrytea said:This is what I have gotten so far:
ΔE = ΔK + ΔU
I previously calculated the ΔU to be 30.25 J
ΔK = Ki- Kf
= 1/2m1v12- 1/2m1v12+1/2m2v22
= 1/2(15.0)(8.00)^2 - 1/2(15)(8.00)^2+1/2(15.0)(2)^2 = 480 - 510 = -30
ΔE = ΔK + ΔU
ΔE = -30 + 30.25 = 0.25 ??
I am super confused at this point and don't know how to continue.
What am I doing wrong?
Blocks? There is only one block and one stone though. So, in your equation what would m2 be?kuruman said:At maximum compression the blocks are moving together with speed V which you have not found yet. Then ΔK=½(m1+m2)V2-½m1v12 where v1 = initial speed of the stone.
It is still not crystal clear, but as I read post #9 the stone rebounds at 2m/s immediately after the collision. The bodies do not coalesce.kuruman said:At maximum compression the blocks are moving together
Sorry, it was way past my bedtime when I posted this. I meant block m2 and stone m1.berrytea said:Blocks? There is only one block and one stone though. So, in your equation what would m2 be?
Yes, the stone rebounds at 2 m/s after the collision is complete. It is not crystal clear what the starting and ending points of the change in ME are. My initial interpretation was from the onset of the collision to after its completion. In post #9 OP revealed that there is more to the problem statement than initially posted. Then in #13 OP confirmed that the change in ME is from the onset to maximum compression. Perhaps if OP posted the entire problem statement as was given, it might become crystal clear what we are looking for.haruspex said:It is still not crystal clear, but as I read post #9 the stone rebounds at 2m/s immediately after the collision. The bodies do not coalesce.
Mechanical energy is the sum of kinetic energy and potential energy in a system. Kinetic energy is the energy of motion, while potential energy is the energy stored in an object due to its position or configuration.
Mechanical energy is calculated by adding the kinetic energy and potential energy of a system. Kinetic energy is calculated as 1/2 * mass * velocity^2, while potential energy is calculated as mass * gravity * height.
A collision is an event where two or more objects come into contact with each other and exert forces on each other. In the context of mechanical energy, a collision typically involves a change in the kinetic energy and potential energy of the objects involved.
The change in mechanical energy during a collision can be calculated by subtracting the initial mechanical energy from the final mechanical energy. This can be determined by calculating the kinetic energy and potential energy of the objects before and after the collision and then subtracting the initial values from the final values.
The change in mechanical energy during a collision is affected by factors such as the mass and velocity of the objects involved, the angle and direction of the collision, and any external forces acting on the objects. The type of collision (e.g. elastic or inelastic) also plays a role in determining the change in mechanical energy.