Unit 3 check
Unit 3 check: Work, Energy, and Power
10 questions from 5 lessons in Unit 3. Answer each one, and if you miss, follow the link back to where it is taught, then try again. Your score counts first tries.
Question 1 · from 3.1 · Calculate
A 0.40 kg soccer ball leaves a player's foot at 15 m/s. What is its translational kinetic energy just after the kick? Give your answer to the nearest joule.
Question 2 · from 3.2 · Calculate
A worker pushes a crate 4.0 m across a warehouse floor, pushing horizontally in the direction the crate moves. She starts with a 50 N push, and as she tires her push falls steadily to 20 N at the end of the 4.0 m. How much work does her push do on the crate?
Question 3 · from 3.3 · Multiple choice
A satellite orbits a planet at a distance from the planet's center. With the zero at infinite separation, the gravitational potential energy of the satellite-planet system is J. The satellite is moved out to a distance from the center. What is the system's gravitational potential energy now?
Question 4 · from 3.4 · Sort it
Each card describes a motion and names a system. Tap a card, then what happens to that system's mechanical energy.
Stays constant
Changes because of work from outside
Is dissipated inside the system
Setup for question 5
A gym class runs a stair test. Each student runs up the same staircase, which rises 6.0 m vertically, and a coach times the climb. For each student, count only the gain in gravitational potential energy of the student-Earth system, and ignore any change in kinetic energy.
| Student | Mass (kg) | Time to climb (s) |
|---|---|---|
| Priya | 48 | 4.0 |
| Marcus | 80 | 7.0 |
| Lena | 65 | 5.0 |
| Owen | 70 | 6.5 |
Question 5 · from 3.5 · Multiple choice
Using the stair-test table, for a staircase that rises 6.0 m: which student increases the gravitational potential energy of the student-Earth system at the greatest average rate?
Question 6 · from 3.1 · Decide and justify
A 0.50 kg ball is thrown straight down from a balcony at 6.0 m/s. Take up as positive, so the ball's velocity as it leaves the hand is m/s. A student writes the ball's translational kinetic energy at that moment as J. Is the student right?
Which reason supports your answer?
Question 7 · from 3.2 · Decide and justify
A student pushes a 20 kg box 3.0 m across a carpeted floor with a horizontal push, at a steady walking speed the whole way. A classmate says the student's push did no work on the box, since the box's kinetic energy never changed. Did the student's push do work on the box?
Which reason supports your answer?
Setup for question 8
A new situation. A box comes down from a balcony, and two people keep track of it, each with a different zero. Decide first whose change is bigger, then practice the two calculations with new numbers each time.
Question 8 · from 3.3 · Decide and justify
A 4.0 kg box is carried down from a balcony 9.0 m above the street to the street. Ana sets the gravitational potential energy of the box-Earth system to zero with the box at street level. Ben sets it to zero with the box at the balcony. How do the sizes of the changes in gravitational potential energy they each find for the trip down compare?
Which reason supports your answer?
Setup for question 9
A new view of a fall. Instead of comparing the two ends, follow the energy meter by meter on the way down. Then practice with a falling stone or a spring launch, with new numbers each time.
Question 9 · from 3.4 · Sketch the graph
A 0.50 kg ball is dropped from rest from 8.0 m above the ground, with air resistance negligible. Take the ball and Earth as the system. Sketch the ball's kinetic energy against the distance it has fallen, from 0 to 8.0 m. The first point is fixed at 0.
One shape that fits
Drag a point up or down, or tap it and use the arrow keys. The shape is checked, and the graph must pass through the values the question gives.
Question 10 · from 3.5 · Match
Tap each situation, then the power your hands deliver to the box or cart.
0 of 10 answered.