• Support PF! Buy your school textbooks, materials and every day products Here!

Finding weights on other planets

  • #1
Finding weights on other planets URGENT

yeah, here comes a hw problem my class had that both me and my friends couldnt get. please help us :bugeye:

A bag of sugar weighs 5.00 lb on earth. what should it weigh in newtons on the moon, where the free-fall acceleration is 1/6 that of earth. repeat for jupiter, where g is 2.64 times that on earth. find the mass of the bag of sugar in kilograms at each of the three locations.

The book answer is 3.71N, 58.7M, 2.27Kg

What just happened. can anyone walk me through this. My e-mail is madperseid@yahoo.com, and my aim sn is themadperseid. Thanks
 

Answers and Replies

  • #2
James R
Science Advisor
Homework Helper
Gold Member
600
15
Weight is mg, where m is the mass and g is the gravitational acceleration.

For example, if an object has mass 5 kilograms, and is on a planet with g=10 m/s^2, then it weighs 50 Newton.

The problem is getting you to think about the difference between mass (the amount of stuff in an object) and weight (the force of gravity on an object).

You need to know that the freefall acceleration on Earth is 9.8 m/s^2. You'll also need to convert pounds to Newtons. (I don't know the conversion factor for that, since I live in a country which uses sensible units. I think pounds are a unit of weight, not mass, though.)
 
  • #3
Diane_
Homework Helper
390
0
James R said:
I think pounds are a unit of weight, not mass, though.)
Depends on the system. In one version, pounds are force and mass is in poundals. In a more common system, there is the pound-force and the pound-mass: one pound-mass weighs one pound-force under one standard g.

And people say those aren't sensible units! Hmph.
 
  • #4
riru, i hope u read this this morning. IVE GOT IT. ok, so here goes

w=mg
thus 5lbs=m*(9.8m/s^2)
since 5lbs is not ci units, convert, using the ratio that 1n=.2248lb
the conversion turns 5 lbs into 22.24n
22.24n=m*(9.8m/s^2)
due to the nature of n (kg*m/s^2), you can divide out g [m/s^2], leaving only the kg mass of the bag on earth (22.7 kg)
then, since w=mg
you merely substitute the mass in, and multiply the gravity by the given ratio
example for moon (2.27kg*((9.8)*(1/6)))=3.7N
For the Jupiter one, you do the same, and multiply the gravity by the given ratio
example for jupiter (2.27kg*((9.8)*(2.64)))=58.7n
 
  • #5
Diane_
Homework Helper
390
0
I didn't bother to check the arithmetic, but you've got the concept down. Bravo!
 

Related Threads for: Finding weights on other planets

Replies
2
Views
15K
Replies
9
Views
868
  • Last Post
Replies
2
Views
7K
  • Last Post
Replies
4
Views
3K
  • Last Post
Replies
7
Views
3K
  • Last Post
Replies
5
Views
9K
  • Last Post
Replies
4
Views
4K
Top