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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Why are wet things darker?


When something gets wet, it usually appears darker. Why?
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A ball is thrown vertically upwards

A ball is thrown from ground level vertically upwards with an initial velocity of vi. Draw a velocity-time graph of the ball’s motion. Consider collisions with the ground are absolutely elastic and neglect air resistance.

Image By Michael Maggs Edit by Richard Bartz – Own work, CC BY-SA 3.0, Link
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A block is attached to a spring


A 15 kg block is firmly attached to a very light horizontal spring (k = 550 N/m) and resting on a smooth horizontal table. Suddenly it is struck horizontally by a 3 kg stone travelling with a velocity of 8 m/s to the right, whereupon the stone rebounds at 2 m/s to the left. Find the maximum distance that the block will compress the spring after the collision.

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