Due: See Website for Due Date s2

PLC Activity #9

Energy Bar Diagrams

Due: see website for due date

How to get credit for this activity

First, sign-in at the computer and sign-out when the activity is complete. Show your work and results to a PLC tutor so they can check your work and initial the signoff sheet. Be prepared to answer questions about the activity or your results.

Question 1

Identify the energy transformations in each of the following processes (e.g. K → Ug → Eth)

a.  A helicopter rises from the ground at constant speed.

b.  An arrow is shot from a bow and stops in the center of its target.

c.  A pole vaulter runs, plants his pole, and vaults up over the bar.

Question 2

A heavy object is released from rest at position 1 above a spring. It falls and contracts the spring at position 2. The spring achieves maximum compression at position 3. (a) Fill in the table below to indicate whether each of the quantities are +, −, or 0 during the intervals 1→2, 2→3, and 1→3 and (b) draw a bar diagram for each position. Explain your answer.

1→2 / 2→3 / 1→3
∆K
∆Ug
∆US

Question 3

Three balls of equal mass are fired simultaneously with equal speeds from the same height above the ground. Ball 1 is fired straight up, Ball 2 is fired straight down, and Ball 3 is fired horizontally. (a) Rank in order, from largest to smallest, their speeds v1, v2, and v3 as they hit the ground. Explain your answers. (b) Draw an energy bar diagram for balls 1, 2, and 3.

Question 4

A block slides from A to C along a frictionless ramp, and then it passes through horizontal region CD, where a frictional force acts on it. Is the block’s kinetic energy increasing, decreasing, or constant in (a) region AB, (b) region BC, and (c) region CD? (d) Is the block’s mechanical energy increasing, decreasing, or constant in those regions? (e) Draw energy bar diagrams for AB, BC, and CD.