A planet follows an elliptical orbit that brings it as close as 21 million km to a star and as far as 75 million km from the star. At both of these locations the velocity of the planet makes a right angle to the direction to the star. If the planet's speed is 38 km/s when it is farthest from the star, how fast is it moving when it is closest to the star

Explanation:

In an elliptical orbit , the angular momentum of the planet remains constant because velocity of planet makes a right angle to the direction to the star .

mvr = constant .

mv₁r₁ = mv₂r₂

v₁r₁ = v₂r₂

v₁ x 21 = 38 x 75

v₁ = 135.71 km/s .

cell differentiation  is how generic embryonic  cells  become specialized  cells. this occurs  through a process called gene expression. gene expression is the specific combination of genes that are turned on or off (expressed or repressed), and this is what dictates how a  cell  functions.

explanation:

wavelength divides in half and speed stays the same.