1. A) Sally's displacement is 5m less than her distance travelled.
Explanation:
- Distance is the total distance travelled by Sally, regardless of her direction. In this case, Sally has travelled 10 meters forward and then 5 meters backward, so the distance travelled is
- Displacement, instead, is the difference between the final position and the initial position of Sally, which means that we have to calculate the vector sum of all the movements made by Sally. Assuming 'forward' as positive direction, this means that Sally's displacement will be:
(forward)
Therefore, we can conclude that Sally's displacement (5 m) is 5 m less than her distance travelled (10 m).
2. B) acceleration due to gravity is always the same
According to Newton's second law:
by re-arranging it, we find the acceleration of an object:
(1)
The only force acting on an object in free fall is the gravity, so , where m is the mass of the object and g is the acceleration due to gravity. Substituting into (1):
So, the acceleration of an object in free fall does not depend on the mass of the object, but only on the value of g, which is the same for every object.