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The capacitance of a two parallel plates capacitor both of area A separated by a distance d is calculated by the area of overlap of the two plates, ... more

A capacitor is an electrical/electronic device that can store energy in the electric field between a pair of conductors. The simplest capacitor consists of ... more

Capacitance is the ability of a body to store an electrical charge. Any object that can be electrically charged exhibits capacitance. Capacitance is a ... more

In electronics, a vacuum tube, an electron tube, or colloquially a tube (North America) or valve (British usage), is a device that controls electric ... more

A uniform electric field is produced by placing a potential difference (or voltage) across two parallel metal plates. A uniform field is one in which the ... more

The dynamic (shear) viscosity of a fluid expresses its resistance to shearing flows, where adjacent layers move parallel to each other with different ... more

The Townsend discharge is a gas ionization process where free electrons, accelerated by a sufficiently strong electric field, give rise to electrical ... more

Shear rate is the rate at which a progressive shearing deformation is applied to some material. The shear rate for a fluid flowing between two parallel ... more

The Townsend discharge is a gas ionization process where free electrons, accelerated by a sufficiently strong electric field, give rise to electrical ... more

Moment of inertia is the mass property of a rigid body that determines the torque needed for a desired angular acceleration about an axis of rotation. ... more

Mass moment of inertia measures the extent to which an object resists rotational acceleration about an axis, and is the rotational analogue to mass. Moment ... more

A capacitor is an electrical/electronic device that can store energy in the electric field between a pair of conductors. Its capacity depends on the ... more

Chladni’s law, named after Ernst Chladni, relates the frequency of modes of vibration for flat circular surfaces with fixed center as a function of ... more

A supercapacitor (SC) (sometimes ultracapacitor, formerly electric double-layer capacitor (EDLC)) is a high-capacity ... more

A supercapacitor (SC) (sometimes ultracapacitor, formerly electric double-layer capacitor (EDLC)) is a high-capacity ... more

Capacitance is the ability of a body to store an electrical charge. Any object that can be electrically charged exhibits capacitance. Concentric or ... more

In science, buckling is a mathematical instability that leads to a failure mode.

When a structure is subjected to compressive stress, buckling may ... more

Moment of inertia is the mass property of a rigid body that determines the torque needed for a desired angular acceleration about an axis of rotation. ... more

Due to leakage of fluid between the back surface of the impeller hub plate and the casing, or through other pump components – there is a volumetric ... more

Lenz’s law /ˈlɛnts/ is a common way of understanding how electromagnetic circuits obey Newton’s third law and the conservation of energy. ... more

First proposed by Clement D. Child in 1911, Child’s law states that the space-charge limited current (SCLC) in a ... more

Capacitance is the ability of a body to store an electrical charge. Any object that can be electrically charged exhibits capacitance. The capacitance is a ... more

Connected in series, the capacitors each store instantaneous charge build-up equal to that of every other capacitor in the series. The total voltage ... more

Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential. Here we can calculate for Stored Energy ... more

Electric potential energy, or electrostatic potential energy, is a potential energy that results from conservative Coulomb forces and is associated with ... more

Capacitance is a measure of the amount of electric charge stored (or separated) for a given electric potential. Here we can calculate for Stored Energy ... more

The first image shows how helicopters store large amounts of rotational kinetic energy in their blades. This energy must be put into the blades before takeoff and maintained until the end of the flight. The engines do not have enough power to simultaneously provide lift and put significant rotational energy into the blades.

The second image shows a helicopter from the Auckland Westpac Rescue Helicopter Service. Over 50,000 lives have been saved since its operations beginning in 1973. Here, a water rescue operation is shown. (credit: 111 Emergency, Flickr)

Strategy

Rotational and translational kinetic energies can be calculated from their definitions. The last part of the problem relates to the idea that energy can change form, in this case from rotational kinetic energy to gravitational potential energy.

Solution for **(a)**

We must convert the angular velocity to radians per second and calculate the moment of inertia before we can find **E _{r}** . The angular velocity

**ω**for

**1 r.p.m**is

and for **300 r.p.m**

The moment of inertia of one blade will be that of a thin rod rotated about its end.

The total I is four times this moment of inertia, because there are four blades. Thus,

and so The rotational kinetic energy is

Solution for **(b)**

Translational kinetic energy is defined as

To compare kinetic energies, we take the ratio of translational kinetic energy to rotational kinetic energy. This ratio is

Solution for **(c)**

At the maximum height, all rotational kinetic energy will have been converted to gravitational energy. To find this height, we equate those two energies:

Discussion

The ratio of translational energy to rotational kinetic energy is only **0.380**. This ratio tells us that most of the kinetic energy of the helicopter is in its spinning blades—something you probably would not suspect. The **53.7 m** height to which the helicopter could be raised with the rotational kinetic energy is also impressive, again emphasizing the amount of rotational kinetic energy in the blades.

Reference : OpenStax College,College Physics. OpenStax College. 21 June 2012.

http://openstaxcollege.org/textbooks/college-physics

Creative Commons License : http://creativecommons.org/licenses/by/3.0/

Coulomb’s constant, the electric force constant, or the electrostatic constant (denoted ke ) is a proportionality constant in equations relating ... more

The speed of light in vacuum is the speed at which all massless particles and changes of the associated fields (including electromagnetic radiation such as ... more

The cross section is an effective area that quantifies the intrinsic likelihood of a scattering event when an incident beam strikes a target object, made ... more

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A typical small rescue helicopter, like the one in the Figure below, has four blades, each is

4.00 mlong and has a mass of50.0 kg. The blades can be approximated as thin rods that rotate about one end of an axis perpendicular to their length. The helicopter has a total loaded mass of1000 kg.(a)Calculate the rotational kinetic energy in the blades when they rotate at300 rpm.(b)Calculate the translational kinetic energy of the helicopter when it flies at20.0 m/s, and compare it with the rotational energy in the blades.(c)To what height could the helicopter be raised if all of the rotational kinetic energy could be used to lift it?