In the lecture videos, we discussed the possibility of calculating the velocity

Question

In the lecture videos, we discussed the possibility of calculating the velocity of the block by using three steps: ()F- - kAx, to find F (2) F = ma, to find a, and then (3) u2-v = 2, to find u Which of the following reasons best describes why this approach is INCORRECT? The value of k is changing throughout the problem, but equation (1) assumes that it is constant. There should not be a minus sign in equation (1), because the block was moved in the positive c direction The force on the block is not zero in this problem, and equation (2) only applies when the net force is equal to zero. We assumed in equation (3) that the initial velocity is zero, but this cannot be true because a block bouncing back and forth on a spring is in constant motion. The acceleration is changing throughout the block's motion, and equation (3) does not apply to such a situation. When we plugged the force into eqution (2), we neglected the force of gravity.

Explanation / Answer

Ans

The force F is not constant (spring constant k is a fix number), Force changes with x, so does the acceleration.

The equation (3) can be used when the acceleration is constant. We can't use equation (3) because acceleration is changing throughout the block's motion. Hence option 5 from top is the right answer.

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