a stone is dropped vertically into a lake which one of the following statements best describes the motion of the stone at the instant it enters the water?a)Its velocity and acceleration are both downwards b)It has an upwards velocity and a downward acceleration c)Its velocity and acceleration are both upwards d)It has a downward velocity and an upward acceleration
the instant it hits the water, it slows down, due to the force of friction at impact. That upward force reduces speed, thus a negative accleration (ie, upward acceleration).
Well, let's dive into this question! When a stone is dropped vertically into a lake, let me tell you, it's quite a splash! Now, to answer your question, at the instant the stone enters the water, we need to consider the forces acting on it.
Gravity, my friend, certainly pulls objects downward. So, we can safely eliminate options (b) and (c), as they suggest an upward velocity and acceleration.
Now, let's focus on the remaining two options. If we think about it, when the stone enters the water, it's losing its upward velocity. That means it's moving downward, so we can eliminate option (c), which says both the velocity and acceleration are upwards.
Therefore, the best description of the stone's motion at the instant it enters the water is option (a): Its velocity and acceleration are both downwards. It's sinking like a stone, quite literally!
The correct answer is d) It has a downward velocity and an upward acceleration.
When a stone is dropped vertically into a lake, its initial velocity is downward due to the force of gravity. As it enters the water, it experiences an upward force, which opposes its downward motion. This upward force causes the stone to decelerate and eventually come to a stop. Since the stone's velocity is still downward at the instant it enters the water, its velocity is downward. However, the stone experiences an upward acceleration due to the upward force from the water.
To determine the best description of the motion of the stone at the instant it enters the water, we need to understand the forces acting on it and the effects of these forces.
When a stone is dropped vertically (from rest), the only force acting on it is the force of gravity pulling it downwards. As it enters the water, there are no other significant forces involved.
Let's analyze the given options:
a) Its velocity and acceleration are both downwards:
Since the only force acting on the stone is gravity pulling it downward, its velocity and acceleration will indeed be downwards. So, option a) is a possible description of the motion.
b) It has an upwards velocity and a downward acceleration:
Since gravity is pulling the stone downwards, it cannot have an upwards velocity. So, option b) is not accurate.
c) Its velocity and acceleration are both upwards:
Again, since gravity is pulling the stone downwards, it cannot have an upwards velocity or acceleration. So, option c) is not accurate.
d) It has a downward velocity and an upward acceleration:
Considering that the force of gravity is the only significant force acting on the stone, its velocity will indeed be downward. However, because there are no other significant forces causing an upward acceleration, option d) is not accurate.
Based on our analysis, the best description of the motion of the stone at the instant it enters the water is that its velocity and acceleration are both downwards (option a)).