Question

joshua programs a robotic arm to place a block in a box by following the sequence of commands in the table

step	command
2	lift block ten centimeters
3	hold for twenty seconds
4	release block

during which step does the robotic arm do work on the block?
step 1
step 2
step 3
step 4

Explanation:

Step1: Recall work - definition

Work is done when a force causes a displacement in the direction of the force, $W = F\times d\times\cos\theta$ ($\theta$ is the angle between force and displacement).

Step2: Analyze Step 1

In Step 1, the robotic arm grips the block. There is no displacement of the block in the direction of the gripping force, so no work is done.

Step3: Analyze Step 2

In Step 2, the robotic arm exerts an upward force to lift the block a distance of ten centimeters. There is a displacement in the direction of the force, so work is done.

Step4: Analyze Step 3

In Step 3, the robotic arm holds the block for twenty seconds. There is no displacement of the block while the force is applied, so no work is done.

Step5: Analyze Step 4

In Step 4, the robotic arm releases the block. There is no force applied by the arm during the release process to cause a displacement, so no work is done.

Answer:

B. Step 2