What is the approximate "weight" of an astronaut on the Moon, if his mass is 80 kg?      A. 128 N B. 784 N C. 50 N D. 176 N

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Weight can be thought of as the gravitational pull a celestial body exerts on a given object or body and hence is dependent on the celestial body in question. In comparison, mass is a measure of the matter contained in the body and is a constant quantity. Since weight is a force, it can be calculated using Newton's second law of motion as:

F = m x a

where F is the force, m is the mass of the body and a is its acceleration. To calculate the weight, you must know the acceleration due to gravity. Acceleration due to gravity is a function of the celestial body the astronaut is on and hence weight will be different on each celestial body. The acceleration due to gravity on Earth is represented by "g" and has a value of about 9.8 m/s^2. In comparison, the value of acceleration due to gravity on the Moon is about 1/6 g and has a value of 1.6252 m/s^2. Hence the weight of the astronaut will be:

weight = mass x acceleration due to gravity

= 80 kg x 1.6252 m/s^2 = 130 N (approximately).

Among the given options, only choice (A) 128 N is close enough and hence is the correct choice.

Hope this helps. 

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