Homework problems with Newton’s laws and force

[FrankP]

Ok so I have not really had any problems with the homework and or sample problems to date, however this homework assignment my teacher has struggled to explain to us for whatever reason so my notes are very all over the place. This homework is not graded however it serves as our test review which will be on Monday so I want to figure this out ASAP so I can begin to practice them.  Using the formulas that I currently have I would not be able to solve this unless I’m overlooking something. Thank you in advance. 

 

P.S. there should be 2 images attached 

[swansont]

Have you learned Newton's gravitational law?

[FrankP]

The F=G(m1*m2/r^2) equation? Yea I have learned by that but struggling to understand the application here because doesn’t that determine the force of attraction of two objects with specific masses? In example 21 what is the dummy mass that I would use to calculate the force of attraction initially? I could do it for tomorrow the 65kg person but part one I can’t figure it out. 

 

And for 30 I looked up the question on google first and it appears they are arbitrary calculations so it doesn’t help me. 

 

Thanks again 

[Mordred]

Try using that equation and determine the acceleration at the radius provided for 21. You don't require a dummy mass for part 1. You should be able to find the accereration at any radius by applying the equation you provided. As you are already given the mass of Mars.

 

 

Edited October 4, 2017 by Mordred

[swansont]

Acceleration can be found by using F=ma in addition to the gravitation law. Simplify the formulas before worrying about numbers, and you will find you don't need the mass.

[FrankP]

Ok as soon as I get home I’ll post my work and see if I have the right methods thank you guys I figured I was overthinking the problem because I have not had issues with the math or logic yet... so usually it’s just me making things harder on myself I appreciate it 

[FrankP]

Ok was able to get an answer which would seem to be correct logically however the only question I have is why is the answer to part one considered to acceleration force of g on mars and not the force? The book states a=3.75m/s^2 I got F=3.75N in the future should I become conditioned to understand that this will be the gravitational force in m/s^2 as opposed to N?

Edited October 5, 2017 by FrankP

[Mordred]

A Newton is defined as " One newton is the force needed to accelerate one kilogram of mass at the rate of one metre per second squared in direction of the applied force"

https://en.m.wikipedia.org/wiki/Newton_(unit)

compare the SI unit of force to the SI unit of acceleration. The only difference is the addition of mass via unit kg.

 

[FrankP]

Thank you for the help my homework ended up being right now time to prepare for the test! haha