Final answer:
The weight of an object at one Earth radius above the surface is a quarter of its weight on the surface due to the inverse square law of gravitation. The weight decreases from 100 N to b) 25 N.
Step-by-step explanation:
The weight of an object is determined by the gravitational force acting on it and is calculated using the formula w = mg, where m is the mass of the object and g is the acceleration due to gravity. On Earth's surface, g is approximately 9.80 m/s². When an object is moved to a point one Earth radius above the Earth's surface, the new distance from the centre of the Earth is twice the Earth's radius. Since gravitational force (and thus weight) decreases with the square of the distance from the centre of the Earth, the new weight W' can be calculated using the inverse square law. The new weight is reduced by a factor of 2² (or 4), so the new weight W' will be 1/4 of the original weight. Therefore, if the object originally weighs 100 Newtons on Earth, it will weigh:
W' = 100 N / 4 = 25 N
So, the correct answer is b) 25 N.