When a lunar module landed on the moon, it used thrusters to slow its descent to the surface. when other spacecraft are returned to earth, they use parachutes to slow their descent. why wouldn't a parachute be useful on the moon?

Two steel balls, each of mass m, are welded to a light rod of length l and negligible mass and are initially at rest on a smooth horizontal surface. a horizontal force of magnitude f is suddenly applied to the rod as shown. determine (a) the instantaneous acceleration a of the mass center g and (b) the corresponding rate at which the angular velocity of the assembly about g is changing with time.

Contains chemical energy. a. heat b. light c. natural gas

Derive the lens makers formula for convex les?