Two adjacent students stand on stationary skateboards, face each other, and push apart. The skateboarder on the left weighs 55 kg, the one on the right is
65 kg. If the lighter skateboarder moves at 4.2 m/s, determine the speed and
direction of the heavier skateboarder.

What would the difference of spectral lines emitted by hydrogen gas in distant galaxies which is normally found at a wavelength of 21 cm on earth, be observed at 21.1 centimeters?

Suppose that a comet that was seen in 563 a.d. by chinese astronomers was spotted again in year 1951. assume the time between observations is the period of the comet and take its eccentricity as 0.986. what are (a) the semimajor axis of the comet's orbit and (b) its greatest distance from the sun?

70 give a real life example showing how sensory neurons work with the motor neurons