# Tagged Questions

Interaction between two or more bodies that results in physical contact and an exchange of momentum between the bodies involved.

1answer
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### Using the central equation for inelastic collisions entropy change

I have what appears to be a simple question but I seem to be missing something. Take a constant temperature system where a ball travelling at $5ms^{-1}$ strikes a stationary ball and sticks to it in ...
2answers
185 views

### What exactly will happen if a small planet collides with earth

This is a video of a simulation of Ceres (a dwarf planet) hitting Earth at 2000km/s. What strikes me the most, is how fast the shockwave is moving. It takes about 6 minutes for the shockwave to pass ...
1answer
46 views

### Difference between sudden force and impulsive force? [duplicate]

What is the difference between a sudden force which continues to act on the body, and an impulsive force? What would be respective speeds of the body just after time= 0?
2answers
193 views

### Elastic collisions and 90 degrees angles [closed]

Why is it that if the angle between the two objects that collided together is 90 degrees then it must be perfectly elastic? Is there any theoretical proof other than convention?
1answer
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### The ratio of masses in an elastic collision [closed]

Two blocks of mass $M_1$ and $M_2$ moving along a 1-dimensional straight line with velocities $V_1$ and $V_2$, respectively, collide elastically. After the collision they move with respective ...
1answer
28 views

### When to consider friction as an impulsive force?

Suppose a ball obliquely strikes a rough horizontal surface then it experiences a frictional impulse and conservation of linear momentum cannot be done on the horizontal direction. Now consider ...
1answer
81 views

### Collision with a stationary Hydrogen atom [closed]

Can some explain me what happens when an electron or neutron collides with stationary Hydrogen atom? What are conditions for elastic and inelastic condition? For example, how to tackle following ...
1answer
42 views

### Calculating the Coefficient of Restitution Based on two Objects

The coefficient of restitution is calculated based on the velocities of objects before and after a collision: $$C_R = -\frac{v_{2f} - v_{1f}}{v_{2i} - v_{1i}}$$ The coefficient of restitution tells ...
1answer
36 views

### How do these particles sort themselves by size? [duplicate]

I have this bowl of sodium polyacrylate (Insta-Snow) that has been drying out for a few weeks. At this point it consists of solid pieces ranging in size from 3 or 4 mm across to much smaller ones ...
1answer
19 views

### Spheres collide with merry-go-round [closed]

Four spheres, with uniform densities $\rho_1, \rho_2, \rho_3, \rho_4$ and radii $r_1, r_2, r_3, r_4$, respectively, roll without slipping with constant velocities $v_1, v_2, v_3, v_4$ along tracks ...
1answer
20 views

### Physics of Auto Crashes and Airbag Modules

I recently saw a post (that was pretty old) asking why we don't consider the jerk function more often in sciences that deal with impacts or sudden accelerations. The general belief was that impacts, ...
2answers
67 views

### Does inelastic collision say the ball bounces back to you when thrown at an angle on ground?

I created a bounce simulation using exactly the formula from Wikipedia. The behavior I observe is not what I would expect in two cases: When two balls hit off-centre, they act the same as if the ...
1answer
714 views

### How do I derive the formula of coefficient of restitution?

I have learnt in collision mechanics about the term Coefficient of restitution, $\mathrm{e=\frac{v_{2f}-v_{1f}}{v_{1i}-v_{2i}}}$. But the sad part is that, in my book only the formula is there. My ...
1answer
35 views

### How do black holes join each other? [duplicate]

If black holes can swallow any object, and can radiate energy, then how could black holes join each other and can form bigger black holes?
2answers
5k views

### Inelastic collision and conservation of linear and angular momentum

Is it possible for two spheres (a & b) to have an inelastic collision with BOTH the total linear and angular momentum preserved? I'm doing some physics simulation of some spheres attracting each ...
2answers
96 views

### How can work be done during collisions? [closed]

Consider a collision between two material points, with no external forces acting on the system. Linear and angular momentum of the system are always conserved, while the kinetic energy of the system ...
2answers
91 views

### Where all those particles come from - proton proton collision

I was reading an article about the "Higgs factory" China is planning to build and it got me thinking about what happens when two protons collide. I am an engineer so I have a good understanding of ...
7answers
534 views

### Why isn't momentum conserved in this pulley problem?

I have some conceptual doubt about method of solving this problem. 24. A block of mass $m$ and a pan of equal mass are connected by a string going over a smooth light pulley as shown in figure (9-...
3answers
110 views

### Car Crash Question… (Conservation of Momentum?) [duplicate]

Dumb car crash question. I think this is a conservation of momentum problem. In one scenario, two 4000 lb cars (car A and car B) each traveling at exactly 35 MPH in opposite directions have a ...
2answers
133 views

### Explicit Function for Bouncing Ball [closed]

I was wondering if it's possible (and if so, how would you go about it) to write an explicit function for the position of a ball bouncing as a function of time (assuming a coefficient of restitution 0 ...
4answers
183 views

### Does the physical cross section of a projectile have an effect on the motion of a target? [closed]

Why can a baseball (moving with kinetic energy) move a baseball glove (or how a hammer displaces a nail),. yet a bullet can't move a person? I know the laws of conservation of energy, deformation, etc....
1answer
81 views

### Technique to Solve 2-Dimensional Linear Momentum Problem

Problem: After a completely inelastic collision, two objects of the same mass and initial speed stick together and move away at half their initial speed. Find the angle between their initial ...
1answer
56 views

### Instantaneous Velocity after bouncing off a wall

I have a ball, and I throw it at a wall as a projectile (assume that the ball's position the instant the journey begins is on level-ground). The ball hits the wall with a velocity that is at right ...
1answer
32 views

### What decides distribution of momenta and energy in rigid collisions?

I recall in Highschool physics receiving a problem of the form "assume 2 spherical bodies" $P_1, P_2$ enter a collision where $P_1$ has momentum $m_1 V_1$ and $P_2$ has momentum $m_2 V_2$, both ...
1answer
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### Collision of moving large mass and small stationary mass?

Hypothetically if a mass, roughly the size of earth, was accelerating at 100m/s and came in contact with a 1kg stationary mass, due to newtons 3rd law wouldn't the small mass accelerate and the large ...
2answers
84 views

### Total Momentum in the Center of Mass Reference Frame

For solving problems involving elastic collisions it is useful to use the center of mass reference frame as to avoid quadratic equations. However, I am confused about why the total momentum in the ...
1answer
91 views

### What is the probability of two bullets to get clashed? [closed]

I was surfing on Instagram, and I found this amazing proto whose description is "the probability of such an event to happen is incredibly small, so this is a really curious finding". Well.. I'm ...
4answers
95 views

### Gravity and force

I have a question and am not able to answer it. Suppose you drop two objects from different heights. They are exactly the same shape, size and weight. Now we know that the gravitational acceleration ...
11answers
53k views

### How can momentum but not energy be conserved in an inelastic collision?

In inelastic collisions, kinetic energy changes, so the velocities of the objects also change. So how is momentum conserved in inelastic collisions?
0answers
39 views

### What is the magnitude of a collision force?

First off, I want to clarify that when I refer to collision, I mean the situation in which two particles cannot be at the exact same position in the space. When two particles get closer and closer, ...