about light

1. what is light?
2. if there is a radio broadcasting on the frequency of 789 MHz, what is a wavelength of this radio waves?
3. why is light make a straight motion in every media which she move in?
4. what is interference?
5. what is difraction?
6. what is a wave characteristics?

Newtons' laws problems

1. An electron (mass = 9.11 X 10- 31 kg) leaves one end of a TV picture tube with zero initial speed and travels in a straight line to the accelerating grid, which is 1.80 cm away. It reaches the grid with a speed of 3.00 X 10 6 m/s. If the accelerating force is constant, compute (a) the acceleration; (b) the time to reach the grid; (c) the net force, in newtons. (You can ignore the gravitational force on the electron.) 

Atwood's Machines

Two masses m1 and m2 connected ot each other using a string and hang them via a pulley as shown at the above figure.