When an object that has been thrown into the air reaches its maximum height, which is true?
a. its velocity is zero.
b. it is at its terminal velocity.
c. it is not in free fall.
d. its acceleration is zero.
Its velocity is zero.
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When an object that has been thrown into the air reaches its maximum height, the correct statement is:
a. Its velocity is zero.
At the maximum height, the object's vertical velocity becomes zero momentarily. This occurs because the object's initial upward velocity gradually decreases due to the force of gravity acting against it. Once the object reaches its peak, gravity pulls it back downwards, causing its velocity to increase in the opposite direction.
To determine the correct answer, we need to understand the physics involved when an object is thrown into the air. When an object is thrown upwards, it experiences two main forces: gravity pulling it downwards and the initial throwing force pushing it upwards.
Let's break down the options to find the correct one:
a. Its velocity is zero: As the object reaches its highest point, it momentarily comes to a stop before changing direction and falling back down. At this point, its velocity is indeed zero for an instant, so option a is correct.
b. It is at its terminal velocity: Terminal velocity refers to the maximum velocity an object can achieve due to air resistance. However, when an object is thrown upwards, it has not yet reached its maximum velocity and is still accelerating against gravity, so option b is incorrect.
c. It is not in free fall: Free fall refers to the state of an object falling under the influence of gravity without any other forces acting upon it. While the object is moving upwards, it is still subject to the force of gravity, so it is technically in free fall. Therefore, option c is incorrect.
d. Its acceleration is zero: During the object's ascent, gravity is acting against its motion, causing it to decelerate. At the maximum height, just before changing direction, the object's velocity is momentarily zero, but the force of gravity still acts upon it. Thus, the object experiences acceleration due to gravity, so option d is incorrect.
Therefore, the correct answer is:
a. Its velocity is zero.