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, $W = F\times d\times\cos\theta$ (where $\theta$ is the angle between force and displacement).

Step2: Analyze Step 1

In Step 1 (Grip block), there is no displacement of the block, so work done is 0.

Step3: Analyze Step 2

In Step 2 (Lift block ten centimeters), a force is applied by the robotic - arm to lift the block against gravity and the block is displaced in the direction of the force. So work is done.

Step4: Analyze Step 3

In Step 3 (Hold for twenty seconds), the block is stationary, so there is no displacement and work done is 0.

Step5: Analyze Step 4

In Step 4 (Release block), the robotic - arm just stops applying the holding force, there is no force applied by the arm causing a displacement, so work done is 0.

Answer:

B. Step 2