Astudent pulls on a 20 kg box with a force of 50 n at an angle 45 degrees relative to the horizontal. the box increases
speed at a rate of 1.5 m/s2. what is the approximate value of the friction force on the box?
50 n
35.4 n
30n
5.4n

Amichelson interferometer operating at a 600 nm wavelength has a 3.02-cm-long glass cell in one arm. to begin, the air is pumped out of the cell and mirror m2 is adjusted to produce a bright spot at the center of the interference pattern. then a valve is opened and air is slowly admitted into the cell. the index of refraction of air at 1.00 atm pressure is 1.00028.how many bright-dark-bright fringe shifts are observed as the cell fills with air?