Need clarification: conservation of kinetic energy (elastic collision)

AI Thread Summary
In an elastic collision, the conservation of kinetic energy is expressed as Ek1i = Ek1f + Ek2f, where the initial kinetic energy of the moving block equals the sum of the final kinetic energies of both blocks. The equation V1i + V1f = V2i + V2f is not valid in this context. Instead, one can manipulate the kinetic energy equation to show that m_1(v_1^2 - v_{f1}^2) = m_2v_{f2}^2. It is important to remember that while the 1/2 can be canceled, the masses and squares cannot be simplified in the same way. Understanding these principles is crucial for accurately analyzing elastic collisions.
tambourine
Messages
17
Reaction score
0
if a block in motion hits one at rest, Ek1i = Ek1f + Ek2f

could i also use V1i + V1f = V2i + V2f?
 
Physics news on Phys.org
No, you can't say that. If you have \frac{1}{2}m_1 v_1^2 = \frac{1}{2}m_1 v_{f1}^2 + \frac{1}{2}m_2 v_{f2}^2 the most you can do is cancel out the 1/2s because there's no way you can cancel out the masses (or the squares).
You could say m_1(v_1^2-v_{f1}^2) = m_2v_{f2}^2
 

Thread 'Errors and significant figures'

I multiplied the values first without the error limit. Got 19.38. rounded it off to 2 significant figures since the given data has 2 significant figures. So = 19. For error I used the above formula. It comes out about 1.48. Now my question is. Should I write the answer as 19±1.5 (rounding 1.48 to 2 significant figures) OR should I write it as 19±1. So in short, should the error have same number of significant figures as the mean value or should it have the same number of decimal places as...
View full post »
Thread 'Collision of a bullet on a rod-string system: query'

Thread 'Collision of a bullet on a rod-string system: query'

In this question, I have a question. I am NOT trying to solve it, but it is just a conceptual question. Consider the point on the rod, which connects the string and the rod. My question: just before and after the collision, is ANGULAR momentum CONSERVED about this point? Lets call the point which connects the string and rod as P. Why am I asking this? : it is clear from the scenario that the point of concern, which connects the string and the rod, moves in a circular path due to the string...
View full post »
Thread 'A cylinder connected to a hanging mass'

Thread 'A cylinder connected to a hanging mass'

Let's declare that for the cylinder, mass = M = 10 kg Radius = R = 4 m For the wall and the floor, Friction coeff = ##\mu## = 0.5 For the hanging mass, mass = m = 11 kg First, we divide the force according to their respective plane (x and y thing, correct me if I'm wrong) and according to which, cylinder or the hanging mass, they're working on. Force on the hanging mass $$mg - T = ma$$ Force(Cylinder) on y $$N_f + f_w - Mg = 0$$ Force(Cylinder) on x $$T + f_f - N_w = Ma$$ There's also...
View full post »

Similar threads

How to Calculate Speed of Head of Driver After Collision?
Replies
10
Views
2K
Question about two elastic collision formulas
Replies
6
Views
2K
Confused about a conservation of energy problem
Replies
4
Views
2K
What Happens to Sphere Velocities After an Elastic Collision?
Replies
1
Views
4K
Two dimensional Elastic Collision
Replies
2
Views
1K
Air-Track Carts & Spring (Energy)
Replies
17
Views
6K
Conservation of momentum - with understanding
Replies
2
Views
2K
Why is momentum conservation always true in a collision?
Replies
4
Views
2K
Bobsled Impulse and Force -- ELASTIC collision problem
Replies
10
Views
2K
Glancing elastic collision, and center of mass
Replies
17
Views
4K

Hot Threads

Recent Insights

Back
Top