Landing of Apollo on moon?

Question

How Apollo’s speed was controlled for its safe landing of on lunar surface. As there is no atmosphere and hence can’t be landed like a chopper.
Again its take off speed is very low and should be decreases because of moon’s gravity until another rocket fired in opposite direction for thrust. And I notice from the video there was nothing left at bottom of Apollo for the next thrust. So why Apollo did not decelerate by the moon’s gravity after certain height.
And how did Apollo was accelerated after take off as acceleration is the rate of change of velocity which can only be possible in empty space by firing rocket from time to time.
A thrust of 3500 lbs was used for LM take off on lunar surface . How did the design engineers calculate the final design speed on the basis of 3500 lbs thrust and moon’s gravity at rendezvoused with CSM in lunar orbit. Or what was its final design speed at the rendezvoused with CSM in lunar orbit.

Answer 1

>>How Apollo’s speed was controlled for its safe landing of on lunar surface. As there is no atmosphere and hence can’t be landed like a chopper.<<

Please do some basic research. The Apollo Lunar Module landed with a rocket engine firing to control its speed.

>>Again its take off speed is very low<<

EVERY rocket takes off slowly. Look at the shuttle. It takes several seconds just to get to the top of the launch tower, yet by the time it gets to orbit it's doing 17,500mph.

>>and should be decreases because of moon’s gravity until another rocket fired in opposite direction for thrust.<<

There was a rocket firing for thrust. The ascent stage, the bit that took off from the Moon, has a rocket engine on the bottom that is firing all the time you see it in the video of the liftoff. You don't see a bright flame because of the fuels used and the fact that it is firing in a vacuum.

>>And I notice from the video there was nothing left at bottom of Apollo for the next thrust.<<

Sorry, wrong. There is an engine there, you're just looking for the wrong thing. Again, some research into the design of Apollo would be helpful.

>>So why Apollo did not decelerate by the moon’s gravity after certain height.<<

See above. There's a rocket firing all the way to orbit.

>>And how did Apollo was accelerated after take off as acceleration is the rate of change of velocity which can only be possible in empty space by firing rocket from time to time. <<

It was firing, all the way. If you watch the Apollo 17 liftoff from the Moon, the ascent stage rises up and then tips over, at which point you are looking right down the neck of the engine, and it is clearly glowing brightly as it fires.

>>How did the design engineers calculate the final design speed on the basis of 3500 lbs thrust and moon’s gravity at rendezvoused with CSM in lunar orbit. Or what was its final design speed at the rendezvoused with CSM in lunar orbit.<<

I'm not a rocket engineer, so I couldn't tell you exactly how they calculated everything, but by the time of Apollo this was a well-practised science.

Answer 2

"How Apollo’s speed was controlled for its safe landing of on lunar surface. As there is no atmosphere and hence can’t be landed like a chopper." The Apollo craft used rockets to land and to take off - rockets are used to take off and land craft anywhere there is a gravitational field (such as Earth, the moon, Mars, asteroids, etc.).

"Again its take off speed is very low and should be decreases because of moon’s gravity until another rocket fired in opposite direction for thrust. And I notice from the video there was nothing left at bottom of Apollo for the next thrust. So why Apollo did not decelerate by the moon’s gravity after certain height." Not sure what you mean by all this - they used rocket engines to slow their descent until they landed, and they used rocket engines to take off. Rockets can continue to provide thrust away from the surface until the craft reaches orbit (just like spacecraft leaving Earth continue to thrust until orbit).

"And how did Apollo was accelerated after take off as acceleration is the rate of change of velocity which can only be possible in empty space by firing rocket from time to time." Again, they used rocket engines to provide the change in direction and velocity as required.

I think you need to do some research for yourself - nasa.gov would be a place to start.
And perhaps some reading on the basics of rocket propulsion.