If i want to accelerate a mass of 3 kg at 5 m/s2 then how much force should i apply?

The force that must be applied is 15 N.

Explanation:

Force exerted on the object is defined as the product of mass of the object and the acceleration of the object.

Mathematically,

where,

F = force exerted = ?

m = mass of the object = 3 kg

a = acceleration of the object =

Putting values in above equation, we get:

Hence, the force that must be applied is 15 N.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)