cq1_08_2 solution and discussion

The following is a solution to the given problem.

Please compare the given solution with your solution and submit a self-critique of any error(s) in your solutions, and/or and additional questions or comments you might have.

Simply copy your posted document into a text editor and insert revisions, questions, and/or self-critiques, marking your insertions with ####. Submit using the Submit Work Form.

How much net force is required to accelerate a 12 kg mass at 3 m/s^2?

The net force would be

F = m a = 12 ks * 3 m/s^2 = 36 kg m/s^2 = 36 Newtons.
Note that the details of the units calculation are necessary and important.

What would be the acceleration of a 4 kg mass subject to a net force of 20 Newtons?

A 4 kg mass subject to a 20 N force would accelerate at

a = 20 N / (4 kg) = (20 kg m/s^2) / (4 kg) = 5 m/s^2.
again not the necessity of unit calculations at every step.

If you exert a force of 20 Newtons on a 10-kg object and it accelerates in the direction of your force at 1.5 m/s^2, then how do you know there are other forces acting on the object besides your own?

If a 10 kg object accelerates at 1.5 m/s^2, then the net force on the object is

F_net = m a = 10 kg * 1.5 m/s^2 = 15 kg m/s^2 = 15 N.

If your force was the only one acting on the object, then the net force on it would be 20 N and it would be accelerating at 2 m/s^2, not at 1.5 m/s^2.

What is the total of all those forces and in what direction does this total act?

If you are exerting a force of 20 Newtons on the object and the net force is only 15 Newtons, this means that the other forces acting on the object must total -5 Newtons. That is, there has to be a 5 N force opposing you.

The following is a solution to the given problem.

Please compare the given solution with your solution and submit a self-critique of any error(s) in your solutions, and/or and additional questions or comments you might have.

Simply copy your posted document into a text editor and insert revisions, questions, and/or self-critiques, marking your insertions with ####. Submit using the Submit Work Form.

The net force would be

F = m a = 12 ks * 3 m/s^2 = 36 kg m/s^2 = 36 Newtons.

Note that the details of the units calculation are necessary and important.

A 4 kg mass subject to a 20 N force would accelerate at

a = 20 N / (4 kg) = (20 kg m/s^2) / (4 kg) = 5 m/s^2.

again not the necessity of unit calculations at every step.

If a 10 kg object accelerates at 1.5 m/s^2, then the net force on the object is

F_net = m a = 10 kg * 1.5 m/s^2 = 15 kg m/s^2 = 15 N.

If your force was the only one acting on the object, then the net force on it would be 20 N and it would be accelerating at 2 m/s^2, not at 1.5 m/s^2.

If you are exerting a force of 20 Newtons on the object and the net force is only 15 Newtons, this means that the other forces acting on the object must total -5 Newtons. That is, there has to be a 5 N force opposing you.