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# Tag Archives: change

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## Rotational motion – Flywheel problem

The flywheel has mass m & is rotating with angular velocity w.the radius of the flywheel is R. masses m1 & m2are placed over r1 & r2 radius.find the change in w due to the placing of masses?

Posted by Tushar Srivastava

(Waiting for your responses before posting the final solution)

## A simple numerical on momentum

Car mass is 1200 kg moving velocity is 108 km/hr. On applying brakes velocity reduced to 36 km/hr. Find change in momentum?

m=1200 kg

u=108 x 5/18=30m/s

v=36×5/18=10m/s

Change in momentum = m(v-u) = 1200 x (30-10)=1200 x 20= 24000 kg m/s

## A simple numerical on momentum

Car mass is 1200 kg moving velocity is 108 km/hr. On applying brakes velocity reduced to 36 km/hr. Find change in momentum?

m=1200 kg

u=108 x 5/18=30m/s

v=36×5/18=10m/s

Change in momentum = m(v-u) = 1200 x (30-10)=1200 x 20= 24000 kg m/s

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## Why gravitational force of attraction is necessary for a satellite to revolve around earth?

The question was posted by Raj Kumar.

The satellite has a velocity. To revolve around, the direction of velocity must change. In the absence of a force it can move only in a straight line. It is the gravitational force which helps the satellite top change direction and revolve around the earth.

In other words, for a satellite to revolve in a circular path, a centripetal force is required. This centripetal force is provided by the force of gravitation only.

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## Explain IMPULSE in simple terms

Impulse is the effect of a force and is measured as the change in momentum produced.

The same effect, that is the same change in momentum can be produced by a large force acting for a short interval of time, a small force acting for a large interval of time or a moderate force acting for a moderate interval of time.

In all these cases the impulse will be the same as the change in momentum will be the same.

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## The mechanism of operation in a capacitor

The DC doesnt flow through capacitor. I thought it was because the electrons jus get saturated on one side and are lost on other side, such that it can’t take or give up anymore or plausibly due to voltage developed across it whereas in AC as directions keep changing, saturation doesnt occur. But it if it were so then AC would flow through two plates seperated by large distances or switches which can be considered capacitors.So please guide me as to what’s actually happening during current flow through capacitor and how it happens? (The question was posted by Thushar Misra)

Your logic is almost correct. A capacitor is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When there is a potential difference (voltage) across the conductors, a static electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field.

A current is not “flowing” through a capacitor, the “current” that exists between the plates of a capacitor is called “Displacement current” which is actually caused by the time varying electric flux. This causes the circuit to be continuous though there is no electrical contact or flow of charges between the plates of the capacitor.

When a capacitor is connected to DC, there exists a change in electric flux when the switch is just turned on but soon it reaches steady state and there is no “current”. A capacitor can “conduct” only when there is a “change” in electric flux, which is continuously taking place in an AC.

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## Tested Physics Links to Learn the Laws of Motion online

Newton’s Laws of motion

First Law: Every body continues to be in its state of rest or state of uniform motion in a straight line unless an external force complels it to do so.

Second Law: The rate of change of momentum of a body is directly proportional to the net external force acting on it and the change in momentum takes place in the direction of motion

Third Law: To every action there is an equal and opposite reaction

The following links will help you learn the topic further and will provide an online resource for understanding the concepts related to it.