easy physics problem I CAN'T FIGURE OUT!

[samser]

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ARG I can't figure this problem out! It's a physics problem from ch 2 of the exam krackers book.

The question is: How much would a 100 kg man weigh on the moon?
a. 17N
b. 100 N
c. 170 N
d. 1000 N

It gives the mass of the earth as 5.97 x 10 ^24 and radius as 6,378

the moon as 7.5 x 10^22 and radius as 1,738

Is there an easy way to do this? This is so frustrating because it's literally a plug and chug problem!

 

[MedPR]

ARG I can't figure this problem out! It's a physics problem from ch 2 of the exam krackers book.

The question is: How much would a 100 kg man weigh on the moon?
a. 17N
b. 100 N
c. 170 N
d. 1000 N

It gives the mass of the earth as 5.97 x 10 ^24 and radius as 6,378

the moon as 7.5 x 10^22 and radius as 1,738

Is there an easy way to do this? This is so frustrating because it's literally a plug and chug problem!

Well you should know that gravity is less on the moon, so 17N is the easy answer. If you don't know that, you can take the data and equation F=GMm/r^2.

The earth is about 75 times more massive than the moon. Earths radius is also about 3 times the radius of the moon. So earth's gravity is 75/9 times greater than the moon. So the moon's gravity is 10*(9/75). Round 75 to 72, and you get 10*(1/8), or 1.25.

 

[411309]

Simple way: W=mg. It cant be 1,000 N as that's his weight on earth. The moons gravity is roughly 1/6s of earths gravity so it's around 1.6-1.7 m/s. So 100kg*1.7 m/s= 170 newtons.

 

[411309]

Well you should know that gravity is less on the moon, so 17N is the easy answer. If you don't know that, you can take the data and equation F=GMm/r^2.

The earth is about 75 times more massive than the moon. Earths radius is also about 3 times the radius of the moon. So earth's gravity is 75/9 times greater than the moon. So the moon's gravity is 10*(9/75). Round 75 to 72, and you get 10*(1/8), or 1.25.

how are you getting 17? 😵. I think you mean 170.

 

[milski]

Well you should know that gravity is less on the moon, so 17N is the easy answer.

You should also know that 100 kg mass would be 1000 N weight on Earth. 😛 (sorry, that was a really cheap shot but I had to take it)

You could do the math - weight will decrease proportionally to the mass change and inversely proportional to the square of the radius. So lighter Moon will decrease it by 5.97 x 10^24/ 7.5 * 10^ 22 or slightly less than 100 times. Smaller radius will increase it by (6378/1738)^2 or about 3.5^2 or about 12 times. Total 100/12 = 25/3 or about 8-ish times less and that's really an overestimation. 170 N seems like the best answer.

Or you can know that the Moon has about 1/6 of Earth's gravity and just go for 170.

 

[MedPR]

how are you getting 17? 😵. I think you mean 170.

Oh yea, sorry I read 10kg instead of 100kg man 🙂 10kg man doesn't even make sense.

 

[411309]

Oh yea, sorry I read 10kg instead of 100kg man 🙂 10kg man doesn't even make sense.

Anorexia is a bitch.

 

[MedPR]

Anorexia is a bitch.

Doesn't a leg alone weigh a little less than 10kg?

 

[milski]

Doesn't a leg alone weigh a little less than 10kg?

There were no legs mentioned in the problem.

 

[411309]

Doesn't a leg alone weigh a little less than 10kg?

he can't be a war vet?

 

[MedPR]

he can't be a war vet?

What would a war vet be doing on the moon?

 

[samser]

YES! thanks everyone!!