If you push a crate with a force of 100 n and it slides at a constant speed and in the same direction, how much friction is acting on the crate

100 N

Explanation: Taking into account the second Newton Law the total force applied to any system is equal to the mass *acceleration.In this case the crate moves at constant speed so the accelaration is zero. In order to satisfy this fact, the friction force must be equal the applied force of 100 N .

when two balls of the different masses are dropped from equal height, they reach the ground at the same time .this is because they experience the same acceleration.

the acceleration is independent of mass.

thus when they are dropped they will always maintain the same velocity and travel the same distance (neglect air resistance of course) at the same time.