A150 kg safe on frictionless casters is being raised at 1.20m to the bed of a truck using planks 4m long. the force needed to push the safe up is

The only thing you need to know in order to solve this task is that plank length (which is force x), should equal the increase in potential energy, so what we have now : (mass)* g * (height).
It has to look like that:  
F * 3.0 = 150 x 9.81 x 1.20 
Then solve for F, the result should be in newtones = 588N

Do hope it makes sense.

Longitudinal waves and Transverse waves are mechanical

Explanation:

This is because mechanical waves require a medium. Longitudinal: sound waves need a medium, like air, hence, no sound in space. Transverse: water waves need volume and an area to move.

Electromagnetic waves dont need a medium, that is like light, microwaves, infrared, etc