Question

An astronaut is preparing calculations for a flight to the moon. the combined mass of the crew, all equipment, fuel, and the rockets is 2.8x10^6kg on the launch pad.
a.The rocket's engines produce a combined 35x10^6N of thrust. Is this enough to lift the rocket and its payload? What if the engines produced 30x10^6N of thrust? Would 25x10^6N be enough?
b.What is the minimum force the rocket needs to exert in order to lift off hte ground and accelerate upward?
c.To return to Earth, the crew must take off from the moon, where gravity is one-sixth that of Earth. Since most of the mass of the rocket is fuel, assume that three-fourths of the mass was lost in journey to the moon. How much force does the rocket need to exert in order to lift off the surface of the moon?

Answer 1

Well, if the rocket is to lift off of the launch pad, the thrust pushing up must be greater than the gravitational force pulling down. You have the thrust produced by the engine, now you need the gravitational force.

To get the force acting on a mass, use F = ma. Here, m is the total mass of the ship and payload, and a is acceleration due to Earth;s gravity (9.8 m/s^2). You should be able to understand it from here.