# Tagged Questions

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### Power to suspend a mass in air

How much power is needed to suspend a mass in the air? The four parts below deal with the same problem. I post them all here, should there be some subtle things I didn't see. The textbook problem A ...
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### Max speed as a function of engine power

My question started out as finding the maximum speed of a go kart, taking into account only the drag forces as force opposing the motor. I've done some investigation to find:  F_{drag}=\; ...
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### Optimal speed for the water wheel

The hydroelectricity plants extract the potential energy of highly deployed massive object (water) as it falls down. Without turbine, all that energy would be converted into speed (kinetic energy) at ...
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### Numerical: Work Power Energy [closed]

A particle moves along a straight line. A force acts on the particle which produces a constant power. It starts with initial velocity 3 m/s and after moving a distance 252 m its velocity is 6 m/s. ...
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### Measuring energy when no work is done — comparing push-ups to planks

tl;dr Is there any meaningful (physical) way to compare the energy expended in the exercise of doing $x$ pushups in $t_1$ seconds, vs the exercise of doing the plank for $t_2$ seconds? I'm ...
177 views

### Does gravity exert more “power” when an object is traveling faster?

So, this question arose when I was pondering the meaning of horsepower and torque in cars. I thought of the following question: There is a 1 kilogram weight on planet M. Planet M has no atmosphere ...
436 views

### Relationship between power and max. speed

I'm talking about the maximum speed if let's say I have a car with the power $P = 1000 \text{W}$ and a force of friction of $5 \mbox{N}$ acting in the opposite direction. After some googling I found ...
407 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 ...
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### I'm having trouble wrapping my head around force, and thus acceleration, diminishing with a higher velocity when using a constant power

Here is an hypothetical situation I thought about that I don't understand. Let's say I have 2 identical rockets with a fixed power. These rockets start to race in the same direction using the full ...
265 views

### What does Power really mean?

I've been trying to solve a problem for some time. I have been given conflicting information by both literature, colleagues and people on this very forum. It's a very simple question: What is the ...
182 views

### Power as a Function of Distance

I am interested in trying to understand the meaning of the integral of power with respect to distance. In the case of force, we have the two formulae: $\int F \, \operatorname{d}\!t = \Delta p$ and ...
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### Why isn't the product rule used in the definition of mechanical work?

Mechanical power is normally defined as $P = \mathrm{d}W/\mathrm{d}t$, and work is normally defined as $W = \vec F \cdot \vec x$. Today an undergrad pointed out a confusion he had from Griffiths' ...
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### Does a 27 hp engine output the same amount of energy as lifting a 1 ton stone block almost 3 meters per second?

I’m trying to get a sense of how much energy a 27 horsepower engine outputs. 27 hp $=$ 20 133 watts (joules/second). Potential energy can be calculated as $E = mgh$ where $g = ~9.8\ m/s^2$ on earth. ...
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### There is no electricity at home,I need to light a 15W CFL Bulb.Can I Do it with the help of a hamster? [closed]

We know that i)avg speed of A Hamster is 30km/hr. ii)Avg mass of hamster is 1.5 kg. From the above info: Kinetic energy=1/2 X mass X velocity^2 So, K.E=1/2 x 1.5 x 30 x 30 ...
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### Delivered/Reflected Power by Drive on a Hamiltonian System

Imagine a SHO with a drive F(t). (or in general a Hamiltonian system) What is the power delivered to the system and can we talk about the power reflected? is i am imagining say a MW oscillator ...
2k views

### When driving uphill why can't I reach a velocity that I would have been able to maintain if I started with it?

Consider these two situations when driving on a long straight road uphill: Starting at a high velocity $v_h$, which the car is able to maintain. Starting at a lower velocity $v_l$, and then trying ...
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### Is resistance to motion directly proportional to the speed of a moving object?

Power is known to be equal to the force x velocity (P=FV). Im solving a question that states the following : Car with engine working at 32 kW, mass of 1 tonne, travels at a constant speed of 40m/s ...
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### Mechanics Question: Energy, Work and Power

I'm a pure mathematician by trade, and have been trying to teach myself A-level mechanics. (This is not homework, it is purely self-study.) I've been working through the exercises and have come up ...