Physics (weight/mass) question?

Question

I swear im not just fishing for answers lol i just need some help and my book is not doing the trick..

"what is the weight of a 76kg astronaut on (a)Earth, (b) on the moon (g = 1.7m/s2) and, (c) on mars (g= 3.7m/s2) and (d) in outer space traveling with constant velocity?"

i know that F=mg in this case, and i understand the difference between weight and mass.. I guess im just having trouble understanding... do i use 9.8m/s2 for g when im calculating for earth? cause then i get a really high (unrealistic) weight. and wouldnt weight and mass be the same on earth anyway? lol now im just thinking too much.. ANY help please :)

Answer 1

Yes, use 9.8 m/s^2 for g for Earth. The answer is in N (newtons), not kg. 745N is a perfectly acceptable weight.

I'm sure you can calculate parts b and c yourself, but part d is interesting.

I'm sure the answer they're looking for is 0, but that's not actually correct.

In outer space, travelling in free fall, the astronaut's weight will be 0. However, travelling in free fall is not the same as travelling with constant velocity. For instance, in orbit around a planet you are travelling in free fall but your velocity is constantly changing.

To travel in free fall means that your net acceleration is the same as the local gravitational acceleration - i.e. that the net force acting on you is the same as the gravitational force. Even in outer space, the gravitational force is not zero, so this is not the same as travelling with constant velocity. So the correct answer for (d) will be equal to the magnitude of the net gravitational force on the astronaut at that particular location.

But I'm sure they just want you to say zero. ;-)

Answer 2

In Scientific terms, Mass and Weight have different units but related through the force of Gravity.
Weight is mass(kg) x g (Gravity 9.8m/s²) and the Unit is 'Newtons' (after Sir Isaac). (Newtons are units of Force).
On Earth, (a), 76kg x 9.8m/s² = 744.8 Newtons.
On the Moon (b), 76kg x 1.7m/s² = 129.2 Newtons.
On Mars (c), 76kg x 3.7m/s² = 281.2 Newtons.
(d)..In outer space at constant velocity is 'Free-falling' and the astronaut will be termed as 'Weightless but, his mass (76kg) is unchanged.

Answer 3

For clarity let's get back to the fundamentals. The mass of a body is the quantity of matter the body contains. So for this astronaut, his mass on earth is the same as his mass on the moon and anywhere else he travels to. His weight is different from one gravitational pull system to the other. His weight derives from the force of gravity on his body.
On earth his weight is: (76kg)(9.8m/s/s) = 744.8N
On the moon his weight is: (76kg)(1.7m/s/s) = 129.2N
On mars his weight is: (76kg)(3.7m/s/s) = 281.2N
In outer space his weight is: (76kg)(0m/s/s) = 0N

Answer 4

Yes you use 9.8 for Earth and don't worry about the answer being high. The weight in your answers will be expressed in a unit called Newtons, "NOT pounds."

You are using the SI system in your problem and in this system:
mass = kg,
force/weight = newton
g = local gravitational acceleration (9.8 m/s^2)

If you were using imperial system then:
mass = slugs
force/weight = pounds
g = local gravitational acceleration (it think its about 32 ft/s^2)

Answer 5

Hello erintaylor1995, let us use S = ut + 1/2 g t^2 u = 0, t = 4.1 s and S = 15.2 m So g_p = 2 S / t^2 = 1.84 m/s^2 So weight of the object on the planet = m g_p = 10.1*1.84 = 18.584 N But weight on the earth = m g_e = 10.1 * 9.8 = 98.98 N

Answer 6

for the first part of ur question, multiply the mass of the astronaut by the values of g........ n i think in (d) there is no weight.