De Broglie wavelength of an electron


What is the de Broglie wavelength of an electron that has been accelerated through a potential difference of 100 V?

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What will be needed in order to restore the balance if necessary?

scale1kgiceYou have a beam balance, the kind of scales that tips from one side to the other, depending on the weight on each side. On the left side lies a kilogram of ice. On the right side lies the standard kilogram. The pans are in balance.
After a while all the ice melted.
Does the balance tip to the right, to the left, or does it remain unchanged?
What will be needed in order to restore the balance if necessary?

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An Empire starship fires at Skywalker’s ship


An Empire starship fires a beam of electrons at Skywalker’s ship. Each electron has an initial kinetic energy of 1.6×10−17 J. The Skywalker’s ship has been fitted out with the electrostatic shield technology for defense against electron beam weapons. The electric field of the shield points directly inward. If the electrons stop after travelling 83 m, what is the size of the electric field generated by the ship’s shield? Please ignore relativistic effects.

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A solid sphere rolls down a roof

solid sphere rolls down a roofA solid sphere starts from rest and rolls without slipping a distance of 8 m down a roof that is inclined at 25˚. The roof’s edge is 5 m high from the ground. How far horizontally from the roof’s edge does the sphere hit the ground?

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The force required to hold a water hose

Calculate the force required to hold a water hose of radius 0.04 m when it emits a jet of water at a speed of 20 m/s.

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The surface energy of a liquid drop



The surface energy of a liquid drop is u. It is sprayed into 1000 identical drops. What will be the total surface energy?

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Jar of Flies

jar-of-fliesA scientist weighs a jar of sleeping flies. Then, he shakes the jar to wake them up. While flies are flying in a closed jar, the scientist weighs the jar again. Does the jar weigh less when the flies are flying?

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