Why are wet things darker?

wet

When something gets wet, it usually appears darker. Why?
Continue reading

A ball is thrown vertically upwards

bouncing_ball_strobe_edit
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
Continue reading

A block is attached to a spring

block-spring-stone

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.

Continue reading

The music of the icebergs.

iceberg_in_the_arctic_with_its_underside_exposedThe icebergs hiss and crackle as they drift toward the equator. Why?

Continue reading

How long would it take to fall through the center of the Earth?

450px-9_daughters_hole
We have a hole that leads straight through the center of the Earth. We neglect air resistance and assume that the Earth has uniform density ρ. How long would it take to fall through the center of the Earth and reach the other side of the planet?

Continue reading

A passenger is late for a train

mpzm6jA passenger is late for a train. He stood at a railway station while the accelerating train passed him car by car. The passenger noticed that the last train car passed him for 8 seconds and the previous train car for 10 seconds. How long was the passenger late for the train? You should consider that the train moved with uniform acceleration and the length of the train cars is the same.

Continue reading

What is the surface temperature of the planet?

508439main_pia00007_full
A planet of radius r and mass M has a homogeneous atmosphere (density independent of height). The atmosphere has a height h and the atmosphere’s gas has a molar mass μ.
What is the surface temperature of the planet?

Continue reading