Unit 2 check
Unit 2 check: Force and Translational Dynamics
10 questions from 9 lessons in Unit 2. 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 2.1 · Fill the statement
A sandcastle is built from damp sand. Take the sand and the water in the castle as the system. Tap a blank, then an answer.
The castle keeps its shape, where a pile of dry sand would slump, because of the between the grains. On a hot afternoon the water evaporates, so mass the system, while sunlight carries energy it.
Question 2 · from 2.2 · Fill the statement
You press your palm flat against a wall, and the wall pushes back on your hand. Tap a blank, then a word.
The wall's push on your hand is a force. At the scale of atoms, it is the force between the atoms of your skin and the atoms of the wall, added up over trillions of atoms. Press harder and those atoms are squeezed , so the wall pushes back harder.
Question 3 · from 2.3 · Multiple choice
A boy sits in a wagon at rest on level ground, with his back against the wagon's seat. Without moving in his seat, he pushes forward hard on the wagon's front rail with both hands. Friction on the wheels is negligible. What happens to the wagon?
Question 4 · from 2.4 · Sort it
Each card describes where an observer watches from. Tap a card, then decide whether that observer would find Newton's first law holding there.
An inertial frame
Not an inertial frame
Setup for question 5
A new situation, and this time the force is sideways to the motion. A hockey puck glides east across smooth ice. A player reaches out and taps it with her stick, pushing it due north for a moment. Decide which way the puck accelerates while the stick touches it. Then practice the second law with new numbers each time.
Question 5 · from 2.5 · Decide and justify
A hockey puck slides east across ice where friction is negligible. A player taps it with her stick, pushing it due north for a moment. While the stick is pushing, which way does the puck accelerate?
Which reason supports your answer?
Setup for question 6
A bathroom scale reports one thing: how hard it pushes on whoever stands on it, and a rocket's couch pushes on an astronaut the same way. Take that idea to two places the lesson has not been, the surface of a large planet and a rocket at liftoff. In each, work out what is pushing and what is pulling before you decide how big the push is.
Question 6 · from 2.6 · Draw the forces
A rocket lifts off straight up from its pad, speeding up as it rises. An astronaut lies on her back on a padded couch that faces straight up, and nothing else touches her. Build her free-body diagram, and set each arrow's length to compare with the other.
The dot is the astronaut. One diagram that fits
Pick each force exerted on the astronaut, then choose the way it points and how long its arrow is compared with the others. The arrows are drawn for you.
Setup for question 7
A student pulls a 2.0 kg wooden block across four different level surfaces with a force sensor held level. On each surface she starts from zero and slowly increases her pull, recording the largest reading just before the block starts to slide. Then she keeps the block sliding at a slow, steady speed and records the steady reading.
| Surface | Largest reading before sliding (N) | Steady reading while sliding (N) |
|---|---|---|
| Wood board | 8.0 | 6.0 |
| Felt | 6.4 | 4.6 |
| Sandpaper | 14.0 | 11.0 |
| Rubber mat | 18.0 | 15.0 |
Question 7 · from 2.7 · Calculate
Using the table of the block's force readings, what is the coefficient of kinetic friction between the 2.0 kg wooden block and the felt? Give your answer to the nearest 0.01.
Question 8 · from 2.8 · Fill the statement
Fill in the facts about ideal springs. Tap a blank, then a word.
A spring that needs a bigger force to stretch it by 1 cm has a spring constant. A spring constant is measured in . Compressing an ideal spring by 2 cm instead of 1 cm makes its push as large.
Question 9 · from 2.9 · Spot the error
A roller coaster car goes around the inside of a vertical circular loop of radius . A student finds the slowest speed the car can have at the top and still follow the loop, taking toward the center of the loop as positive. Tap the first line that goes wrong.
Question 10 · from 2.1 · Decide and justify
A family drives 300 km to visit relatives. In the back of the minivan, two kids bounce around and swap seats the whole way. Can the minivan and everyone in it be modeled as a single object to find how long the drive takes?
Which reason supports your answer?
0 of 10 answered.