There is a 5 kg block sitting on the floor. if the block is being pushed horizontally with a force of 33 n and friction between the block and the floor acts with a force of 15 n, what is its acceleration?

If I'm right you bring in newtons second law which is F=ma

you rearrange to a=F/m
so 18/5 (33-15 - unbalanced forces)
acceleration is 3.6m/s squared

Wut 

The  moon has  insufficient gravity to retain an  atmosphere. we conclude that the moon has no atmosphere  because its gravitational field is too weak to  have  retained any  atmosphere  that it had over times comparable to the age of the solar system.