Your 'cq_1_11.1' report has been received. Scroll down through the document to see any comments I might have inserted, and my final comment at the end.
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Answer the following based on Newton's Second Law:
• How much net force is required to accelerate a 12 kg mass at 3 m/s^2?
answer/question/discussion: The Net force required to accelerate a 12 kg mass at 3 m/s^2 is equal to Fnet= m * a =(12 kg) * (3 m/s^2) =36 Newtons.
• What would be the acceleration of a 4 kg mass subject to a net force of 20 Newtons?
answer/question/discussion: Fnet = m * a, so a= Fnet/m= 20 Newtons/4 kg =5 m/s ^2.
• 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?
answer/question/discussion: Knowing that Fnet= F + fFrict, we can write the equation m * a = F + fFrict = (10 kg) * (1.5 m/s^2) = 20 Newtons + fFrict and we can solve for fFrict as -5 Newtons. We know this to be true because 10 kg * 1.5 m/s^2 is 15 Newtons, which is not equal to the force exerted of 20 Newtons.
Good, but you don't know what the nature of the other force is. It isn't necessarily friction, and even if friction is among the forces acting there might be others.
The key is the Fnet = 10 kg * 1.5 m/s^2 = 15 N.
If you are exerting 20 N, then there must be other forces acting whose total is an opposing 5 Newtons.
In symbols, F_net = F_byYou + F_other, where F_byYou is the force you exert and F_other is the sum of all other forces.
Your expression was very similar to this; you used fFrict where the above uses the more general F_other.
• What is the total of all those forces and in what direction does this total act?
answer/question/discussion: The total of all those forces is 15 Newtons, as was calculated for Fnet above (15 N = 20 N – 5 N) and they are going in a positive direction.
Good. The total of forces to which the question refers is the -5 N in your expression.
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It took me about 30 minutes to solve these problems.
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You're doing very well.
See my notes and let me know if you have questions.