Why does rubbing a balloons on wool or hair make it attract other objects

Scientists use laser range-finding to measure the distance to the moon with great accuracy. a brief laser pulse is fired at the moon, then the time interval is measured until the "echo" is seen by a telescope. a laser beam spreads out as it travels because it diffracts through a circular exit as it leaves the laser. in order for the reflected light to be bright enough to detect, the laser spot on the moon must be no more than 1.0 km in diameter. staying within this diameter is accomplished by using a special large-diameter laser. part a if λ = 540nm , what is the minimum diameter of the circular opening from which the laser beam emerges? the earth-moon distance is 384,000 km. express your answer to two significant figures and include the appropriate units.

Which pair of quantities includes one quantity that increases as the other decreases during simple harmonic motion?

City b is south of city a, and the 200 mile trip by car takes 4 hours. the cities are 120 miles apart in a straight line. what is the velocity of a trip from city a to city b?