0
votes
1answer
18 views

Final velocity of a spring [closed]

I need to calculate the velocity of an object when it is thrown by a spring; we have to calculate the velocity from $U=\frac 12 kx^2$. Now I know that $U=L=F\cdot S$ and $S=\frac{v_f^2-v_0^2}{2a}$. ...
4
votes
2answers
183 views

What's wrong with my derivation for the spring constant? [duplicate]

An $8.00\ \mathrm{kg}$ stone at rest on a spring. The spring is compressed $10.0\ \mathrm{cm}$ by the stone. What is the spring constant? I used conservation of energy to solve this problem. The ...
-2
votes
2answers
48 views

Friction between a block resting on top of another pushed block [closed]

A block of mass $m$ is is on top of a block of mass $M$ on a table. A constant horizontal force $F$ acts on the lower block. What is the kinetic friction between the bigger block and a surface? Find ...
-3
votes
0answers
48 views

Find work done by friction given: mass, distance traveled, and the initial and final velocities [closed]

During a game of curling, a 5.7 kg rock is sliding down the ice sheet. It leaves the curler's hand at 3.0 m/s and enters the house at 0.23 m/s a distance of 15 m away. How much work was done by ...
1
vote
1answer
93 views

Work Done in a Thermodynamic System (Cylinder with Piston) [closed]

Heated Piston A cylinder of cross-sectional area 0.0314m^2, filled with argon (a monatomic ideal gas), is sealed with a piston of mass M=25kg that is free to move up and down. The piston is ...
-1
votes
1answer
27 views

how to use the energy work kinetic theorem [closed]

A single force acts on a $3.4~\text{kg}$ particle-like object in such a way that the position of the object as a function of time is given by $x = 4.2t - 2.1t^2 + 2.5t^3$, with $x$ in meters & $t$ ...
0
votes
1answer
64 views

Why does the magnetic force exerted by two charged particles on each other do no work?

An electron and a proton are moving under the influence of mutual forces. In calculating the change in the kinetic energy of the system during motion, one ignores the magnetic force of one on another. ...
3
votes
1answer
98 views

Could $\int (\ddot\phi + \mu\dot\phi^2)d\phi$ ever be negative? How to show it?

I am working on the following problem: Given a mass $m$ at rest at the base of an incline surface shaped like 1/12th of a circle with radius $R$. The mass is pulled up the incline by a rope that ...
0
votes
1answer
23 views

Comparing work done for two accelerations

Suppose at a time $t_{0}$ a car goes from 0 to 30mph at time $t_{1}$, and then maintains a speed of 30mph until $t_{2}$. After that minute it accelerates, reaching 60mph at time $t_{3}$. I want to ...
2
votes
1answer
160 views

Is work is equal to $mv^2$ (without $\frac{1}{2}$)?

I was trying to come up with an equation for work that doesn't include time, because I don't know time. Here's what I did: $$ work = Fd = mad = m{v\over t}d = m{v\over\left({d\over v}\right)}d = ...
0
votes
1answer
30 views

What is the work done below proportional to? [closed]

A raindrop falls from a certain height to the ground, with a terminal velocity u. The viscous force is F = 6*3.14*n*r*v, where n is the coefficient of viscosity, r is the radius of the raindrop, and v ...
0
votes
1answer
150 views

Computing average force exerted by ground when jumping

Problem: A man of mass $m$ jumps vertically into the air from a sitting position in which his center of mass (CoM) is at a height $h_1$. When his feet are just about to leave the ground his CoM is at ...
0
votes
2answers
76 views

Find the minimum force that has to be applied to the block $m_1$ so that the other block just begins to slide

This is a problem from the book 'Problems in General Physics' by I E Irodov. Two blocks of masses $m_1$ and $m_2$ are placed on a rough horizontal surface, connected by a light spring. Find the ...
0
votes
2answers
45 views

Work done by a frictional force on a cylinder

A cylinder of mass $m$ and radius $R$, is rolled on surface with coefficient of kinetic friction $\mu_{k}$ about the axis passing through the center and parallel to the surface, with initial ...
2
votes
4answers
93 views

Is work done by how much velocity is changed or how much displacement is done?

A sailboat is moving at a constant velocity. Is work being done by a net external force acting on the boat? The answer key is "No" according to the work energy theorem about work is done when ...
1
vote
1answer
54 views

Work done in pulling a rope from a boat

A boy sitting on a boat pulls on a rope with a constant force $F$ over a duration of time $t$. The other end of the rope is either tied to a bridge or to another freely floating boat of equal mass. ...
0
votes
2answers
104 views

Work done by magnetic field on magnetic dipole

In the above slide, it reads that $W=\int\mu B sin(\theta)d\theta=\mu B cos(\theta)$. But, I thought that $\int\mu B sin(\theta)d\theta=-\mu B cos(\theta)$ by some calculus calculation. Can ...
0
votes
2answers
73 views

Why is work in a constant electric field equal to the force times distance?

Let's say, for example, that an infinite plate generates a constant electric field that exerts a force of 6N on a 1C charge. To move the charge from a distance of 5m to 1m from the plate, the work ...
0
votes
1answer
60 views

Kinematics and Energy - Finding the work done in projectile motion

If you are asked to find the work done by gravity on a projectile, the force will obviously be the mass multiplied by gravitational acceleration. What will the displacement be, the horizontal or ...
2
votes
3answers
110 views

How do I relate $ds$ to $dx$?

A block of mass $5\text{ kg}$ is kept on an inclined plane with angle of inclination $37°$, attached to a spring with spring constant $10\text{ N/m}$ kept at the base of the incline. The ...
2
votes
1answer
26 views

Minimum Power Required

Here is a question, I found two methods to solve it, differing in the answers and I'm not sure why a method is incorrect. Question: A fire hose of cross section area ...
0
votes
2answers
160 views

Is there a mistake in this example in my mechanics textbook?

This is a worked example in my mechanics book: But I think this worked example is wrong. In the 6th line. shouldn't $X=4R$ as the expression for distance above the surface is $(X-R)$ and when the ...
8
votes
3answers
856 views

Number of planks required to stop the bullet [closed]

A bullet looses (1/n)th of its velocity passing through one plank. The number of such planks that are required to stop the bullet can be? Logically, to me the answer seems to be infinity, as always a ...
-3
votes
1answer
49 views

Work done from force-extension graph [closed]

The answer is C, but I got B... F at 3cm = 10, F at 6cm = 20 $W=F\cdot s$ $(20-10)\times 3=30$ I must have made a mistake or stupid assumption then, how am I meant to get 45 N cm?
1
vote
1answer
74 views

Work done (by gravity) on paired blocks [closed]

Why does gravity do more work on the block going down? The total work done (by gravity) on the $8kg$ block is more than the work done (by gravity) on the lighter block. How?
-1
votes
1answer
71 views

Can someone explain the solution (provided) of this conical pendulum work problem [closed]

In the image, it looks like the tangential direction is always 45 degrees away from the string, not 90 degrees. Is it not the circular path that the solution is talking about?
0
votes
1answer
54 views

Hydrostatics , work Power and Energy [closed]

If a servant lifts 10 cubic meter of liquid from a tank, which is at a depth of 40m . If the work done by him is 1600J, then find the density of the liquid (g = 10 m/s^2)
-1
votes
1answer
67 views

Work Power & Energy Question [closed]

If a person starts from rest with an acceleration of 10 m/s^2 and applies force of 1000N then What will be its work done at the end of 20s . If the object moves in the horizontal surface? Can ...
0
votes
1answer
42 views

To write work capacity of heart by symbols?

I know that the work capacity of the heart is Work capacity of the heart = pumping capacity x aortic impedance. I would mark work by W and impedance by Z. ...
0
votes
2answers
321 views

In Which of the following situations would force be exerted on on object and no work be done on the object?

Consider the following question: In which of the following situations would a force be exerted on an object and no work be done on the object? I. a centripetal force is exerted on a moving ...
1
vote
1answer
2k views

Calculate work done in an inclined plane [closed]

How can you calculate the work done by a force (of unknown quantity) exerted on a 10kg block on an inclined plane. The force is pointing upwards and parallel to the incline (which is inclined 30 ...
0
votes
4answers
267 views

Work is force multiplied by distance What is this distance? [closed]

What is the distance which the force is multiplied by it to get the work done? a) The distance of the body motion while the force was touching it? b) The total distance of the body motion?
0
votes
2answers
71 views

Finding the value of velocity $u$ [closed]

A block of mass $m$ is pushed towards a moveable wedge of mass $\eta m$ and height $h$, with a velocity $u$. All surfaces are smooth. The minimum value of $u$ for which the block will reach the top of ...
0
votes
2answers
164 views

Why does the coefficient of performance need to be calculated with $W + Q$?

How much work must a heat pump with a COP of 2.50 do in order to extract 1.00 MJ of thermal energy from the outdoors (the cold reservoir)? The first formula that came into my mind after reading ...
1
vote
2answers
264 views

Increase in velocity by loss of mass? [closed]

A trolley of mass 300kg carrying a sand bag of 25kg is moving uniformly with speed of 27km/h on a frictionless track. After a while, sand starts leaking out of a hole on the floor of the trolley at ...
0
votes
0answers
72 views

How to relate compression ratio to work input for a compressor in a heat pump

So I need to calculate the COP (Coefficient of Performance) for a 6-ton air conditioner system in terms of the compression ratio. I understand that: $$COP=\frac{Q_L}{W_{net,in}}$$ I cannot find out ...
0
votes
1answer
282 views

Work done on gas by piston [closed]

In this problem there is a cylinder that is closed at both ends and has thermally insulated walls. It is divided into 2 parts by a movable, frictionless, thermally insulated piston. There is a ...
1
vote
0answers
427 views

Work, Energy, Power, Force question [closed]

Question: 3 boys push a small car 25 m up a hill inclined at 19° to the horizontal. The car has a weight of 860 N and they push it at a steady speed of 0.5 m s-1 against an opposing force of friction ...
0
votes
1answer
587 views

Solve a problem of work and energy

A man pulling sled of his daughter by a massless rope, climbing a snowy hill whose slope is equal to 15 °. Considering that the mass of the sled is $4Kg$, the girl's $26Kg$ and $\mu _c = 0,25$, ...
3
votes
1answer
89 views

Work done by vibrating string

figure from http://webusers.physics.illinois.edu/~m-stone5/mma/notes/amaster.pdf The string has fixed ends, a mass per unit length of $\rho$, and is under tension $T$. This source claims that "the ...
5
votes
7answers
2k views

If the net work on a particle is zero, can the speed change?

The following question was on a quiz in physics class: If the net work done on a particle is zero, which of the following statements must be true? a) The velocity is zero b) The velocity is ...
8
votes
3answers
686 views

Bird flying in a cage

Assume that you are holding a cage containing a bird. Do you have to make less effort if the bird flies from its position in the cage and manages to stay in the middle without touching the walls of ...
1
vote
1answer
209 views

A question from a Physics 2 exam: About electron cloud an a constant external field:

I am trying to prepare for my exam in Physics $2$, the following is a question from an old exam (the question also have a detailed answer to it, but I don't really understand it). An acceptable ...
0
votes
3answers
2k views

Work, Energy & Power - Body slides down a hemisphere

A small body of mass $m$ slides down from the top of a hemisphere of radius $r$. There is no friction between the surface of the block and the hemisphere. The height at which the body loses contact ...
2
votes
2answers
440 views

Falling chain with friction

I really need some help with a physics problem, and I guess my doubt is more conceptual, than question based. But still, let me pose it to you: A uniform chain of mass $M$ and length $L$ lies on ...
3
votes
2answers
2k views

work done by tension

The problem statement, all variables and given/known data Consider the following arrangement: Calculate the work done by tension on 2kg block during its motion on circular track from point $A$ to ...
0
votes
1answer
499 views

Is there another way to calculate the work done by air resistance?

A ball of mass $0.37\text{ kg}$ is thrown upward along the vertical with a initial speed of $14\text{ m/s}$, and reaches a maximum height of $8.4\text{ m}$. a) What is the work done by air ...
1
vote
1answer
183 views

Adding heat to a system doesn't equal the work done by gas?

So, I answered a physics question for a class that goes as follows: A gas in a cylinder is kept at a constant pressure of $250000\: \mathrm{Pa}$ while $300\: \mathrm{kJ}$ of heat are added to it, ...
2
votes
1answer
205 views

Work done by gravity on Water

Now according to me we would see change in potential energy of system and equate it to the work done by gravity. But when we see this the first column lowers by $H/2$ and right one rises by $H/2$ ...
0
votes
1answer
85 views

Work done by complex field on complex plane

A force field is given by $F = 3z+5$. Find the work done in moving an object in this force field along the parabola $z = t^2 + it$ from $z = 0$ to $z = 4+2i$. I don't understand why conjugate ...