External force Definition and 56 Threads

The mathematical representation of the net external force on a system(obtained from Newton's second law) is ##\vec F_{net} = \frac {d\vec P}{dt}##, which is the rate of change of linear momentum of the system. If we substitute ##\vec P = m\vec v## into the formula for force and differentiate, we...

I remember, a few weeks ago, when looking for homework problems I could help with, seeing one as described in the title. I couldn't think of an easy solution and was busy at the time so i made a mental note to think about it later. I finally got around to doing that yesterday, and brushed up on...

Suppose we have a system of particles being acted upon by a single external force ##\mathbf{F}^{e}##. Each individual particle feels a force of ##\mathbf{f}_i = \mathbf{f}_{i}^{int} + \mathbf{f}_{i}^{e}## such that ##\sum_i \mathbf{f}_{i}^{e} = \mathbf{F}^{e}##, and ##\mathbf{f}_{i}^{int}## are...

I got this picture from a superconducting parametric amplifier text I was reading. (The picture is a mechanical analog of a non-degenerate parametric amplifier.) If the balls(red and blue) were oscillating at their own natural frequencies, and an external force is driven(purple), how would the...

The figure is shown above. In order to facilitate solution, I need to separate each block and draw the free-body diagram (FBD) with all the forces acting on it. 1. Let me start with the lowest block. Let me put its FBD as shown below. For forces in the vertical direction, ##N_3 = N_2 + m_3 g...

When my professor sums external forces (to know if the impulse is constant or not) he always includes tension. I will use as an example pic related. If my system includes the two particles and the thread, woudn't tension being a internal force? I'm sorry if it's a silly question, but I also...

1.Problem statement Prove the average external force of a system of particles N starting from rest and ending at rest is zero.Homework Equations If the system moves periodically prove the av. external force is zero in a period The Attempt at a Solution I don't quite understand what i am asked...

Homework Statement Homework Equations Seen above The Attempt at a Solution Why is the force acting on block B = N + P + W =0? ? Shouldn't it be B = -P-W+N? So that P = -W+N=0

Why ain't momentum conserved when external force acts on the system? Please explain with an example.

Homework Statement A particle with mass m is undergoing with harmonic motion with a period T, we introduce an external force F proportional to velocity v so that F= -bv with b a constant and we assume that the particle continues to oscillate how does the period change? Homework Equations F= m...

can a resultant external force on a body change its mass but keep velocity of its centre of mass constant ? Is it practically possible - ##\vec{F}_{ext}=\vec{v}_{com}\frac{\mathrm{d} M}{\mathrm{d} t}## where F is nonzero

Homework Statement A ball of mass of 1Kg is held in hand. The moment it is released from hand, without any delay it is hit by an external force of 100N in upwards direction. How high will the body go ? Homework EquationsThe Attempt at a Solution I know how to solve if instead of Force we...

Homework Statement A car attempts to accelerate up a hill at an angle θ to the horizontal. The coefficient of static friction between the tires and the hill is µ > tan θ. What is the maximum acceleration the car can achieve (in the direction upwards along the hill)? Neglect the rotational...

If an electron is brought near the proton from infinity,potential energy of the electron decreases so work done must be positive because the change in potential energy is the NEGATIVE of the work done .But how ?I mean for work done to be positive, force and displacement should be parallel to...

Homework Statement In the picture Homework Equations In the picture attached. The Attempt at a Solution For the firecracker problem, I believe the only net external force is gravity. Therefore using, Fnet * delta t = delta p. Change in momentum is 12 kg * m/s. Thus, the final momentum of the...

I am doing a physics project whose purpose involves describing the physics behind a toy. The toy I have selected is a "decision maker" which is composed of a pendulum which has a magnetically charged ball on it that swings side to side, while having a force exerted on it by magnets which change...

Hi, I'm trying to formulate some general ideas on how systems convert energy imparted by external forces. Could anyone please read the following and see if any of the statements and examples are correct? I really like the idea of thinking of isolated systems as "machines" through which energy...

I was trying to solve this problem yesterday and I was not able to. I looked it up its solution but my mind is not still clear about it. "The work done by an external force to move a -6,5C charge from point A to B is 15J. If the charge was started from the rest and had 4.86J of kinetic energy...

Homework Statement Point charges, Q1 = +56 nC and Q2 = -98 nC, are placed as shown. In Figure 18.1a, an external force transports an electron from point A to point B. The work done by the external force is closest to: A) +620 eV B) -920 eV C) -620 eV D) +920 eV E) +770...

Homework Statement An inflatable membrane is filled with an ideal gas at a pressure of 0.3 bar gauge. The gas is at 40 deg C and the volume of the membrane is 100m^3. The membrane is constrained on all sides and bottom, and a force of F acts on the top of the membrane. The material the...

Hello! :) I have a question..I am given the following exercise: Prove that the motion of a mass m on a linear spring with constant $k$, has the form $y (t) = Asin(wt+f)$ , where $t$ is the time and $A, w, f$ are constants. Interpret the physical meaning of the above constants and specify their...

Homework Statement a rope is used to pull a 3.57kg block at constant speed a distance 4.06m along a horizontal floor. the force on the block from the rope is 7.68 N and is directed 15 degrees above the horizontal. a) calculate the work done by the ropes force b) calculate the increase in...

Homework Statement This problem concerns a collision experiment performed on a frictionless surface with gliders A and B, with masses m(a) and m(b) respectively. In a level track, glider B has a spring-loaded plunger attached to it. At time t(i), glider A moves to the right with speed...

[b]1. A crate is pulled to the right with a force of 82 N, to the left with a force of 115N, upward qith a force of 565N and downward with a force of 236N. [b]2. what is the magnitude and direction of the net external force [b]3. i solved for magnitude(330N) but I am not sure how...

Describe a situation in which the net external force is not zero, but its speed remains constant. I don't know if this situation is possible to explain.

Homework Statement A particle of mass m is attached to a spring (of spring constant k) and has a natural angular frequency ω0. An external force. F(t) proportional to cos ωt(ω ≠ ω0) is applied to the oscillator. The time displacement of the oscillator will be? Homework Equations F=-kx...

I thought I would do a little physics for fun, since it has been over 20 years since I last did any. I picked up Sethna's Stat Mech book. He gives a derivation of the diffusion equation that goes as follows: A particle makes random steps, ie x(t+Δt)=x(t) + l(t). The steps l(t) are given...

Homework Statement A block weighing 70.0 N rests on a plane inclined at 25.0° to the horizontal. A force F is applied to the object at 50.0° to the horizontal, pushing it upward on the plane. The coefficients of static and kinetic friction between the block and the plane are, respectively...

Homework Statement Spheres of masses m1 2.53kg and m27.16kg are fixed at a distance 1.56m apart centre to centre.A m3 212 g sphere is positioned 42cm from the 7.16 kg fromcentre of 7.16 kg sphere along the line of centres.How much work must be done by ext agent to move thesphere of 212 g...

Let us suppose that I have an isolated box which contains some masses connected with springs etc. When this box is stationary in the inertial frame, I can use lagrange's method to solve all coordinates related with the masses and springs without any problem. However, let us also suppose that I...

Homework Statement Homework Equations σ=pr/t (hoop) σ=pr/2t (longitudinal) τ=VQ/It The Attempt at a Solution I have longitudinal stress and hoop stress. I'm trying to find shear stress, which should come only as a result of the 40kN from the collar correct? I'm confused...

Hi there. I was just wondering how does a force actually casue motion of body .. and what are the factors that determine whether the force will cause change in bodies state of motion or direction or its shape? This is what i was thinking about the action of force: A solid body has matter...

Homework Statement A particle of (positive) charge Q is assumed to have a fixed position at P. A second particle of mass m and (negative) charge -q moves at constant speed in a circle of radius r1, centered at P. Derive an expression for the work W that must be done by an external agent on...

Ok, so when a car turns, the tires provide the acceleration pointing toward the center of the turn. If for some reason, I put a spoiler on my car with two rectanglular pieces, one on each side that are tilted, to the left, mocking an airplane rudder, thus when the wind has contact with them...

A 1.6 kg breadbox on a frictionless incline of angle θ = 36° is connected, by a cord that runs over a pulley, to a light spring of spring constant k = 120 N/m, as shown in the figure below. The box is released from rest when the spring is unstrectched. Assume that the pulley is massless and...

Homework Statement A worker pushed a 26kg block 13m across a level floor at a constant speed, with a force directed 40 degrees below the horizontal. If the coefficient of kinetic friction between the block and floor is 0.40, what were a.) the work done by the workers force? and b.) the...

Homework Statement A worker pushed a 16 kg block 6.7 m along a level floor at constant speed with a force directed 32° below the horizontal. If the coefficient of kinetic friction between block and floor was 0.34, what were (a) the work done by the worker's force and (b) the increase in...

Consider a positive charge +q placed at the origin. Let A and b be two points in the space with position vectors rA and rB respectively. What will be the work done by an external force equal and opposite to the Coulumbic force, in moving a unit positive charge from A to B, irrespctive of the...

Suppose I perform an experiment, set up as follows: There is a rotating body which rotates around a vertical axis. The axis is at one end of the rotating body (denoted as the rotator) so that the axis is not through the center of mass of the rotator. The vertical axis is attached to a second...

Hi guys. I am working on making a haptic device for a baseball simulator. Now the problem is that I want to replace the external force for the ball hitting the bat with an internal force in my bat-like device using either solenoids or motors. Do you think it is possible to replace the external...

A dog pulls on a pillow with a force of 7.9 N at an angle if 28.3 degrees above the horizontal \vec{F}_{net} = \Sigma \vec{F} = m \vec{a} A) What is the x component of this force? answer in units of N. B) What is the y component of this force? answer in units of N. help pls i...

1. What is the actual static frictional force that acts on the block if an external force of 25.0 N acts horizontally on the block? ________N The mass of the block is 25.0kg. Assume g=9.80m/s^2 Homework Equations I am using: static frictional force=(coefficient of static...

Homework Statement Homework Equations The Attempt at a Solution To be honest, I have no idea how to start this problem.

Hmm. I'm quite confused with this: Does no resultant force means no external force? i.e. if there is an external force, there is a resultant force? Like say, sand falls onto a moving conveyor belt at the rate of 5.00 kg/s. The conveyor belt is supported by frictionless rollers and moves...

Hey there! I'm faced with this problem: http://img7.imageshack.us/img7/4381/25686658nz9.png It's a 1D nonhomogeneous wave equation with a "right hand side" equaling to the dirac delta function in x * a sinusoidal function in t. I have to find its general solution with the constraints...

Homework Statement How much work does it take for an external force to set up the arrangement of charged objects in the diagram on the corners of a right triangle? Assume that q = -5.2 µC, that d = 19 cm, and that the three objects are initially very far away from each other. Homework...

Homework Statement A crate is pulled to the right with a force of 92.3 N, to the left with a force of 116.8 N, upward with a force of 508.8 N, and downward with a force of 248. 6 N What is the net external force in the x direction? Answer in units of N Homework Equations When I...

Homework Statement Suppose that I1 = I2 = 20 A; currents are running opposite each other, and that the separation between the wires is 0.019 m. By applying an external magnetic field (created by a source other than the wires) it is possible to cancel the magnetic field at the position of each...

Question: A mass of 2kg is suspended from a spring with spring constant k = 4N/m and natural length L = 2m. The mass is also subject to an external downwards force F = 2sin(2t) Newtons. Initially the mass is released at a height 50cm above the equilibrium position. Assume the mass is subject to...

A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat? Explain. The speed of a particle doubles and then doubles again because a net external force acts on it. Does the net force do more work during the first or the second doubling...