Question Video: Acceleration and Force Physics

Video Transcript

How much force is applied to an object of mass five kilograms that is accelerated by that force at a rate of two metres per second squared?

So in this question, we’ve got an object which has a mass — let’s say 𝑚 — of five kilograms and is accelerated — let’s say it’s accelerated to the right — because we can randomly choose a direction. And we’ve been told that this acceleration, which we’ll call 𝑎, is two metres per second squared. We’ve been asked to find the force applied to this object.

Now because the acceleration we’ve said is to the right, this must mean that the force exerted is also to the right, since the force and acceleration must be in the same direction. And we’ll call this force 𝐹.

Now to find the value of this force, we need to recall Newton’s second law of motion. This law tells us that the net force on an object, 𝐹, is equal to the mass of that object multiplied by the acceleration it experiences. So with this equation, we’ll be able to find the net force on the object. And this is exactly what we’ve been asked to find. Even though the question doesn’t necessarily say find the net force, we’ve been asked to find how much force is applied to an object.

Now this may imply that there’s only one force acting on the object, in which case that force is the net force anyway. Or there could be multiple forces acting on the object, but the resultant force or the net force is going to be a combination of all of those forces, whilst accounting for the direction in which they act. And that overall combination can also be thought of as the amount of force applied to an object. And so we can use Newton’s second law of motion to find our answer to this question.

We can therefore say that the force on the object, the net force, is equal to the mass, which is five kilograms, multiplied by the acceleration of the object, which is two metres per second squared. Now taking a quick look at the units, we see that we’ve got kilograms and metres per second squared. And those are the base units of mass and acceleration, respectively. Therefore, when we find our final answer for the force, it’s going to be in its own base unit as well.

Now the base unit of force is the newton, which is equivalent to a kilogram multiplied by metres per second squared. And so when we evaluate our answer — that’s five kilograms multiplied by two metres per second squared — we find that the force is 10 kilograms metres per second squared or 10 newtons. And hence, our answer to this question is that the force applied to this object is 10 newtons.