# Question Video: Acceleration and Force Physics • 9th Grade

An object of mass 1.5 kg has a force of 4.5 N applied to it. At what rate does the force accelerate the object?

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### Video Transcript

An object of mass 1.5 kilograms has a force of 4.5 newtons applied to it. At what rate does the force accelerate the object?

Okay, so here we’re told that we’ve got an object which has a mass of 1.5 kilograms and it has a force of 4.5 newtons applied to it. What we’ve been asked to do is to find the acceleration of the object caused by the force. To do this, we need to recall Newton’s second law of motion.

Newton’s second law of motion tells us that the resultant force on an object, 𝐹, is equal to the mass of the object, 𝑚, multiplied by the acceleration experienced by the object, 𝑎. Now in our case, we’re trying to find out the value of the acceleration experienced by our object. So we need to take Newton’s second law and rearrange it to solve for the acceleration.

To do this, we can divide both sides of the equation by the mass of the object, 𝑚. This way, the masses on the right-hand side cancel out. And so what we’re left with is the net force on the object divided by the mass of the object is equal to the acceleration of the object.

Now what we need to do is to substitute in the values that we’ve been given in the question, first of all the net force on the object. Well, in this case, there’s only one force acting on the object, so the net force is simply the force applied to the object. So the force on the object is 4.5 newtons, and we need to divide this by the mass of the object, which is 1.5 kilograms. And this is equal to the acceleration experienced by the object, at which point we can evaluate the left-hand side of the equation.

And when we do this, we find that the acceleration is three, but three what? What are the units? Well, we’ve been working in standard units for everything so far. For example, we know the force in its standard unit, which is the newton, and we know the mass of the object in its standard unit, which is the kilogram. Therefore, the acceleration will also be in its own standards unit, which is meters per second squared. And hence, we’ve reached our final answer. The rate at which the force accelerates the object is three meters per second squared.