Unit 2 check

Unit 2 check: Force and Translational Dynamics

10 questions from 10 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 · Decide and justify

A diver leaves a springboard, tucks into two somersaults and straightens out before she reaches the water. You want to predict how long she is in the air. Can you model the diver as a single object for this question?

Which reason supports your answer?

Question 2 · from 2.2 · Fill the statement

A sneaker rests on a gym floor. Tap a blank, then a word.

The floor's upward push on the sneaker is a force. At the scale of atoms, it is the total of a huge number of forces between the atoms of the floor and the atoms of the sneaker. Earth's gravitational pull on the sneaker is exerted .

Question 3 · from 2.3 · Sort it

Tap a card, then say whether the tension in that string, rope or chain is the same at every point along it.

Same at every point

Can differ from point to point

Question 4 · from 2.4 · Sketch the graph

A ball rolls off the edge of a level table at 2.0 m/s and falls for 0.50 s before it lands; take the direction it was rolling as $+ x$ , with $x = 0$ at the table's edge. Air resistance is negligible. Sketch the shape of the graph of the ball's horizontal position $x$ against time while it falls.

Drag a point up or down, or tap it and use the arrow keys. Only the shape is checked.

Question 5 · from 2.5 · Rank it

Four carts move on level tracks with negligible friction. Cart A has a mass of 2.0 kg and a net force of 6.0 N on it; cart B, 4.0 kg and 12 N; cart C, 1.0 kg and 2.0 N; cart D, 3.0 kg and 15 N. Rank the carts by the magnitude of their acceleration.

Greatest first

Give each one a place, 1 for first. Give two the same place if they are equal.

Cart A
Cart B
Cart C
Cart D

Your ranking: none yet

Question 6 · from 2.6 · Multiple choice

An astronaut wakes in a closed cabin with no windows. She holds a 2.0 kg wrench and a 0.020 kg pencil level with each other and lets go. Measured from the cabin, both fall side by side toward the floor at 10 m/s². What can she conclude from this alone?

Setup for question 7

A student lays a wooden block on a level board. Hanging the block from a force sensor shows that its weight is 20.0 N. She hooks the sensor to the block and pulls horizontally, gently at first and then harder, until the block starts to slide; then she keeps it sliding at a steady speed. The direction she pulls is positive. The sensor readings:

Force sensor readings while the student pulls the block
$t$ (s)	Pull (N)	Block
0	0.0	at rest
0.5	2.1	at rest
1.0	4.0	at rest
1.5	6.2	at rest
2.0	8.1	starts to slide
2.5	6.1	sliding at a steady speed
3.0	5.9	sliding at a steady speed
3.5	6.0	sliding at a steady speed
4.0	6.1	sliding at a steady speed
4.5	5.9	sliding at a steady speed

Question 7 · from 2.7 · Calculate

Using the readings, what is the coefficient of static friction between the block and the board?

Your answer

Setup for question 8

A student hangs a light spring from a clamp. Its relaxed length is 10.0 cm. She hangs slotted masses from its lower end, one load at a time, and measures the spring's length with a meter stick once the load hangs at rest. Take down as positive and use $g = 10$ m/s². Her readings:

Spring length with each load at rest
Load (kg)	Spring length (cm)
0.10	14.1
0.20	17.9
0.30	22.1
0.40	26.0
0.50	29.9

Question 8 · from 2.8 · Calculate

Using the readings, find the spring constant of the spring as the slope of the best-fit line of force against change in length. Use $g = 10$ m/s².

Your answer N/m

Setup for question 9

A class puts a 0.50 kg fan cart on a level aluminum track with negligible friction. A magnet under the cart produces a braking force ${\vec{F}}_{r} = - k \vec{v}$ , and a force sensor shows that the fan pushes the cart forward with a steady 0.40 N. Take the cart's direction of travel as positive. The cart starts from rest at $t = 0$ , and a motion sensor records its velocity:

Motion sensor readings
$t$ (s)	$v$ (m/s)
0	0.00
0.5	0.32
1.0	0.50
1.5	0.63
2.0	0.69
3.0	0.76
4.0	0.79
5.0	0.79

Question 9 · from 2.9 · Multiple choice

The class adds a 0.50 kg block to the cart and repeats the run from rest, with the same 0.40 N fan force and the same magnet. Compared with the first run, how does the cart's velocity behave?

Question 10 · from 2.10 · Draw the forces

A student swings a pail of water in a vertical circle at the end of a rope. At the very top of the circle the pail is upside down, moving to the left, and the rope is taut. Air resistance is negligible. Build the free-body diagram of the pail and the water together at that instant.

The dot is the pail and the water.

Pick each force exerted on the pail and the water, then choose the way it points. The arrows are drawn for you.

0 of 10 answered.