All Questions
Tagged with conventions newtonian-mechanics
141
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Is gravitational potential energy of body by $mgh$ negative? [closed]
Consider a 15kg object at 1m from earth ground level,
is P.E = 15kg * 9.8m/s^2 * 1m = 147J
or P.E = -Gm1m2/r^2 * h = -9.8 * 15kg * 1m= -147J
after browsing for a while on debate of potential energy's ...
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4
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75
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Why is work done by force $+mgh$ in the situation of throwing something up?
If there is a particle at point A(at rest) and a force moves it to point B(Above point A vertically)(final velocity = 0 at this point), the work done by gravity is $-mgh$. This I understand as the ...
- 85
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7
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Physical Quantities Sign Convention
I see that almost all physical quantities carry signs. But the confusion I have is what they really mean.
Does negative velocity mean decreasing velocity or velocity in the opposite direction?
Does ...
-1
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3
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78
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Sign of work done by spring force [closed]
Two similar springs P and Q have spring constants $K_p$ and $K_q$ such
that $K_p>K_q$. They are stretched by the same amount. Compare the
work done by the springs. (NEET 2015)
$$W_p=-\frac{1}{2}...
- 347
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5
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246
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Work done in raising an object to a height
When we raise an object to a height $h$, it is said that the potential energy of the object is increased by $mgh$. But isn't the work done by gravitational force $-mgh$?
Then that will essentially ...
- 702
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2
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43
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Expression for Potential energy of a hanging mass
If the acceleration due to gravity is $g$ and a mass $m$ is hanging from a fixed support with a thread of length $l$, then it's potential energy ($U$) is given by:
$$U = -mgl;$$
This was stated by my ...
user355398
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1
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116
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The Plus/Minus sign on Forces in a Cartesian coordinate system
I have been struggling with Forces in a Cartesian Coordinate System and whether to understand what signs to put on to solve simple problems in the view of mathematics.
Let's make a simple one ...
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160
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Minus sign in Force potential relation, a convention?
The usual defination of force in terms of potential energy is
$$\vec F=-\nabla U$$
This definition leads to
$$K_1+P_1=K_2+P_2\rightarrow \Delta K + \Delta P =0$$
Where $K$ and $P$ are kinetic and ...
0
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2
answers
133
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Work Done By vs Work Done On
Assuming right to be positive, in this question, is the work done by the boy positive or negative? I would think it is negative because the force that the boy exerts is towards the left while the ...
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1
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75
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What is the significance of a reference point in calculating the potential?
The gravitational potential is given as $$U(r)=-\frac{GMm}{R}$$ where $G$ is the universal gravitational constant $M$ is the mass of the earth and $m$ is the mass of an arbitrary object and $R$ is the ...
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47
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What happens if we define the gravitational potential zero point at a finite distance? [duplicate]
Two questions.
Can we, and if so how do we define the gravitational potential of a mass (say the sun) to be zero at a finite distance (say 1 light year)?
How does this change the gravitational force ...
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1
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64
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Sign convention error in rotational mechanics [closed]
I was recently going through a question regarding the angular velocity of a rod-mass system as a function of angle rotated. Ive given down my working below. My question is, why does the term of ...
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5
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6
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443
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Is the factor of 1/2 in the equation for kinetic energy just due to Coriolis's definition of work as force $\times$ distance?
Variants on this question have been asked repeatedly. See for example:
How did we arrive that kinetic energy $KE = \frac{1}2 mv^2 $?
Why there is a 1/2 in kinetic energy formula?
Coincidence, ...
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1
answer
50
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Convention when considering a mathematical pendulum attached to an object with a spring [closed]
Sorry for the horrible picture, it was the best I could do.
I am trying to find the lagrangian for this set up, but I have problem with the convention of the potential energy, whether it should be ...
- 1,398
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Context behind physical equations and formulas [closed]
In a lot of cases we can sum up our problems with a well defined context such as which variables are 'changing' and which 'constant', in physical formulas we are given none of this so how can we make ...
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