5. Left
Explanation: centripetal acceleration is the acceleration that acts on an object which is moving by circular motion. The direction of the centripetal acceleration is always towards the centre of the circular trajectory: that means that for a car following a bend, the direction of the centripetal acceleration is towards the centre of the bend, and so it is towards the left if the bend is towards the left, and towards the right if the bend is towards the right.
In this example, the road in this bend is going to the left, so centripetal acceleration is toward the left as well.
6. Greater
Explanation: Inertia represents the tendency of an object at staying in motion if it is moving, and at staying at rest if the object is at rest. We can also see inertia as a measure of "how difficult it is" to put an object in motion. Due to this definition, we can also notice that inertia is directly proportional to the mass of the object: the greater the mass, the greater the inertia, because it is more difficult to put the object in motion.
So, in this example, the greater the boulder's mass, the greater inertia it has.
7. Direction
Explanation: displacement is a vector quantity that represents the difference in position between an object and a starting point. Because it is a vector, displacement consists of two elements:
- A magnitude, which is equal to the object's distance from the starting point
- A direction, again compared to the starting point
So, displacement depends on the object's distance and direction from the starting point.
8. Negative
Explanation: acceleration is defined as the rate of change of velocity; in formula:
where v is the final velocity, u the initial velocity, and t the time taken to accelerate from u to v. From the formula, we see that:
- When the final velocity (v) is greater than the initial velocity (u), acceleration is positive
- When the final velocity (v) is smaller than the initial velocity (u), acceleration is negative
In this problem, we have a car slowing down: it means that the final velocity is smaller than the initial velocity, so in this case acceleration is negative.
