# Calculating Rock Speed on Impact from 10m

• Ugnius
In summary, this conversation is discussing how to solve a physics problem. The problem is asking for the speed and height of a rock just before it touches the ground. The solution is that the speed won't stay constant and the rock will drop in speed after it has fallen a certain distance. The solution also assumes that the rock starts at rest.
Ugnius

## Homework Statement

Rock is falling from 10meters 18km/h speed , what is speed of rock just before it touches the ground

## The Attempt at a Solution

So in meters its like 5m/s and h=10m so t=2s if h=d , v=t*d=2s*10m=20m/s but i think i somehow should include gravity too so I am stuck

Ugnius said:
so t=2s
Why?
The speed won't stay constant.
Ugnius said:
v=t*d=2s*10m=20m/s
This formula assumes the rock starts at rest. It does not.

Don't blindly put values into formulas. Think about what is happening and then which formula could be useful.

Conservation of energy is the easiest approach here, using the kinematic formulas (correctly) is possible as well.

mfb said:
Why?
The speed won't stay constant.This formula assumes the rock starts at rest. It does not.

Don't blindly put values into formulas. Think about what is happening and then which formula could be useful.

Conservation of energy is the easiest approach here, using the kinematic formulas (correctly) is possible as well.
How could i use kinetic energy when i have no mass and no energy only height and velocity

The mass will drop out of the calculations.

Mfb is correct.

If my assumptions are correct, you are still in the early stages of learning Physics where mass can often be ignored, mainly just for practice.

Jump into the earlier chapters of your book (if you aren't there already) and skim through any sections that focus on "Particle Under Constant Acceleration."

Just keep in mind that this early stage of physics requires tons of assumptions and ignorance. Don't let it fluster you (read a head and practice with other variables if you are inclined).

I was just watching the Particle Under Constant Acceleration , but there's given time , and acceleration , could you atleast tell me what formulas should i use

As much as I hate doing this, because this is how I was treated, you should find it yourself.

The location of the formula was given, along with the general name of it, and you already know you don't have to worry about mass. I opened my book right up to chapter 2, skimmed, found the name and equation, and posted on this thread. Go for it. It's easy.

Ugnius said:
could you atleast tell me what formulas should i use
That is the point of your (!) homework problem.

Multiplying or adding numbers is something your calculator can do. Figuring out which numbers to multiply or add is the actual physics.

If my calculations were correct should i get 15,15m/s?

My calculations were 14.66, but I did them off the top of my head.

Maybe that's because i took 10m/s^2 and you 9.8m/s^2 this is possible too

That is probably the most likely case.

And just as a heads up, physics is wholly about logical problem solving a dang ton of research. If the research isn't your thing, get better at it or trying a different field (not attempting to deture you).

We won't confirm possible guesses. We don't know w
Ugnius said:
I was just watching the Particle Under Constant Acceleration , but there's given time , and acceleration , could you atleast tell me what formulas should i use
You should become familiar with what are known as the SUVAT equations (look it up!). For kinematic problems such as this you will almost always find that one of the SUVAT equations suits the situation by involving the right mix of variables (the givens and the unknown).

## 1. How is rock speed on impact calculated from a height of 10m?

The rock speed on impact can be calculated using the formula v = √(2gh), where v is the speed, g is the acceleration due to gravity (9.8 m/s²), and h is the height of the drop (10m).

## 2. Can other factors affect the rock speed on impact from 10m?

Yes, other factors such as air resistance, the shape and density of the rock, and the surface it lands on can affect the final impact speed.

## 3. What is the impact speed of a rock dropped from 10m?

Using the formula v = √(2gh), we can calculate that the impact speed of a rock dropped from 10m is approximately 14 m/s.

## 4. How accurate is the calculated rock speed on impact?

The calculated rock speed on impact is an approximation and may vary slightly due to external factors such as air resistance and the shape of the rock. However, it provides a good estimate of the impact speed.

## 5. Can this formula be used for objects other than rocks?

Yes, this formula can be used for any object that is dropped from a height of 10m, as long as the external factors are taken into consideration. However, for objects with irregular shapes or varying densities, the impact speed may differ from the calculated value.

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