# Tag Info

## New answers tagged kinematics

### Angle-free two-dimensional inelastic collision formula?

The direction of the velocities (in a center of mass system) after a collision in two (or three) dimensions will depend on the shape and size of the colliding objects (and their elastic properties). ...
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### A question regarding equations of motion

v=0 after it hits the ground,SUVAT only applies when acceleration is uniform, when it hits the ground acceleration must change from 9.81 to something else, because there is now a new force acting on ...

### A question regarding equations of motion

The body's motion has two very different parts: It begins by accelerating down, until just before reaching the ground. At this point, as you noted, its velocity will be $v=-g*t$ (if the acceleration ...
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1 vote

### How to find time taken for a faster object to cross a slower object of same length, both moving parallel to each other in the same direction?

When solving physical problems it is essential to draw diagrams. This helps to develop a concept in your mind (especially when having no idea yet about the solution). Do this before writing down any ...
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### Angle-free two-dimensional inelastic collision formula?

you can use those equations \begin{align*} &m_1\,(\mathbf v_1-\mathbf u_1)=-\lambda\,\mathbf n\\ &m_2\,(\mathbf v_2-\mathbf u_2)=\lambda\,\mathbf n\\ &\left[(\mathbf v_2-\mathbf{v}_1)+...
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### How to find time taken for a faster object to cross a slower object of same length, both moving parallel to each other in the same direction?

Here you're only trying to find the time taken by this object to cover a distance equal to it's length. So, time=length/speed. Have you been given the speed and length?
Accepted

### Is the deceleration a result of friction, a constant value?

Frictional force=$k$*weight=$k*m*g$ (you need gravity in there to convert mass to weight) So yes, frictional force is proportional to weight which is proportional to mass so deceleration rate is ...
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### Is the deceleration a result of friction, a constant value?

There are two possible friction forces that can cause deceleration: Static friction and kinetic friction. Take the case of deceleration of a car. When you apply the brakes, the torque applied to the ...
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### Is the deceleration a result of friction, a constant value?

It is generally assumed that sliding kinetic friction, $μ_k$N, is independent of speed. On the other hand, fluid friction (with the air or a liquid) does increase with an increase in speed.
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Accepted

### Find the equation for the angle $\theta$ in which the particle leaves the semicircle. No Friction

I don't think this is wrong. $k=0$ represents the case where the large hemisphere has zero mass, so no inertia. I think you are looking for the case where the large hemisphere is "fixed", so ...
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1 vote

### How do we assume the direction of $u_{\theta}$ and $u_{r}$ in polar coordinate systems?

As a rule, $\hat{u}_X$ is always pointing in the direction along which $X$ grows. It works when $X$ is a linear parameter ($x$, $z$, $r$...) as well as when it's an angular parameter ($\theta$, $\phi$....
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1 vote

### How do we assume the direction of $u_{\theta}$ and $u_{r}$ in polar coordinate systems?

The unit radial vector is always away from the origin. The unit tangential vector is always anti-clockwise around the origin such that $\hat{r}\times\hat{\theta}$ is out of the diagram. Not knowing ...

### Projectile with air resistance analysis

With air resistance, typically the horizontal distance is more on ascent, because it loses horizontal speed the whole way.
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### Minimum energy of projectile to trigger a nuclear reaction and energy of ejectiles

Check conditions required for a nuclear reactions. Some easy ones are isotopes of hydrogen or uranium. Tupical energy per particle when reactions is detectable is about 10KeV, which is somewhere ...

### Closing speed and time needed for light to reach moving object

Your approach is not complicated at all, in fact I would suggest you solve any problem like this involving doppler shifts from basics as you did. You will get a hang of it, and if you use closing ...
1 vote

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### Calculate efficiency from discrete power, time and distance

I would recommend doing the third one: $\frac{P_1 + P_2}{2} \times \frac{T}{M}$ for each point, then taking the average of all of them, but throwing out any where: T is greater than 2-3 seconds \$...
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