Tagged Questions
16
votes
2answers
742 views
Why can't Humans run any faster?
If you wanted to at least semi-realistically model the key components of Human running, what are the factors that determine the top running speed of an individual? The primary things to consider would ...
0
votes
1answer
91 views
Energy needed to lift and bring down an object
A mass of 0.5 Kg needs to be moved from point A to another point (B) which is 1 meters above point A. The time for this movement should be 0.2 seconds, then the mass is kept at position B for another ...
-1
votes
2answers
60 views
Changing Direction in a Vaccum [closed]
If a mass of one kilogram is traveling at one meter per second at 90 degrees, how much energy is required to get it to travel going 180 Degrees?
0
votes
2answers
86 views
Can there be energy with no force or energy with no power?
I think that both force (number of newtons) and power (p=ui(?)) implies that there is energy so we can't have force without energy and we can't have power without energy(?)
But can there be energy ...
2
votes
1answer
74 views
Is energy always proportional to frequency?
Google has no results found for "energy not proportional to frequency" and many results for E=hf. Is there an example of an energy that is not proportional to frequency?
1
vote
1answer
58 views
Static Friction work and Energy [closed]
I have this problem:
A 4.0 kg block is given an initial speed of 8.0 m/s at the bottom of a 20° incline. The
frictional force that retards its motion is 15.0 N. (a) If the block is ...
0
votes
1answer
53 views
Potential energy and average force? [closed]
A body of mass $15\,kg$ originally at rest $5\,m$ above the ground falls and penetrates $15\,cm$ into soft earth.
Determine the loss of potential energy
Determine the average
resistance of the ...
2
votes
4answers
498 views
Relationship between mass, energy, and a force?
I've never truly understood the relationship between mass, energy, and force. I know what each of the three are, I just don't fully understand how they interact with each other.
For example,
How ...
7
votes
3answers
551 views
Is the normal force a conservative force?
Most of the time the normal force doesn't do any work because it's perpendicular to the direction of motion but if it does do work, would it be conservative or non-conservative?
For example, consider ...
0
votes
1answer
212 views
A Lawnmower Problem
For my physics class we were just given an exam that asked the following:
A 12Kg lawnmower is pushed with a constant force along the 30* handle with 80N.
Break the Forces into its vector ...
2
votes
1answer
161 views
Would the Moon drift away from the Earth due to extraction of tidal energy? [duplicate]
Possible Duplicate:
Why does the moon drift away from earth?
It seems to me that, due to conservation of energy, the moon would drift away from the Earth if humans began extracting large ...
0
votes
1answer
88 views
Why are there two ways to solve for energy of a spring?
I can find the energy of a spring using $F = -kx$, or by using the formula $e = 1/2mv^2 + 1/2I\omega^2 + mgh + 1/2kx^2$. The first way, I get $mg/k = x$, but the second way, I get $2mg/k = x$. Which ...
0
votes
2answers
182 views
From where does the force/energy of action-reaction comes from? (Newton's Third Law of Motion)
I was wondering, from where does the opposite force and thus energy comes from when we apply force.
For example, lets say there are two persons (P1 and P2) on the universe, and no force is applied to ...
-1
votes
3answers
473 views
Relation between Newtons and Kilograms
Work is expressed as W=F*d, where the F is in Newton, d is in meters and result ...
1
vote
0answers
148 views
Slackline Jump Tension
So a slackline is basically a bouncy tight rope.
I found a site that has a calculator for the tension of a static slackline
...
0
votes
2answers
355 views
From knowing just the change in kinetic energy, can we find the friction force and engine power?
I understand this topic well enough to get all the task done because they aren't very creative. But for my exam I think I should have this clear.
During the acceleration the force from the engine is ...
4
votes
3answers
499 views
Why do we need the quantity momentum?
Why do we need the quantity Momentum in physics when we have the quantities like Force and Energy? Isn't it possible to substitute the usage of Momentum with equivalent of Force and Energy?
2
votes
1answer
352 views
Conservation of Energy in Special Relativity
In classical Newtonian mechanics, from what I understand, conservation of energy stems from the fact that all known forces are conservative forces,
and vector calculus tells us that they can be ...
0
votes
1answer
122 views
Does friction act in the same way in different directions?
A physics textbook is launched up a rough incline with a kinetic energy of $X$ joules. When the book comes momentarily to rest near the top of the incline, it has only gained ($X-20$) joules of ...
0
votes
0answers
97 views
Simple: What do these ballistic impact numbers represent?
I bought physics for game programmers, found here, today to study ballistic impact, but I'm confused as to where a few numbers are coming from. I'm basically looking to understand what the values ...
1
vote
2answers
221 views
Could someone remind me what this means again? $\nabla U = \pm F$
You know that for a potential function (conservative force/fields) that
$\nabla U = \pm \vec{F}$
In math, we don't have that minus sign, we have only the plus one.
What does it mean if you get rid ...
4
votes
3answers
2k views
Force as gradient of scalar potential energy
My text book reads
If a particle is acted upon by the forces which are conservative; that is, if the forces are derivable from a scalar potential energy function in manner $ F=-\nabla V $.
I ...
2
votes
2answers
203 views
Small scale water power, how does water volume and hight convert into electric energy?
I was playing a little bit with the basic physics behind water power production but I can't get the numbers right.
Let's say that I put a windmill that pumps water into a watertank on the top of my ...
2
votes
1answer
1k views
calculating thermal energy [exam prep]
I'm preparing for a grade 11 physics exam but having trouble with a question:
a 19.9kg mass slides in a straight 28.8m line
experiencing friction with a coefficient of 0.105, how much thermal energy ...
