Momentum and Collisions: Is It Conserved?

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Science · Physics
SP-PHYS-006 · Free to print and use in your classroom · substituteplans.com
Page 2
Momentum and Collisions: Is It Conserved?
Science · Physics · Grades 10-12 · 50 minutes
Time needed
50 minutes (one class period)
Prep
Copy the 2-page worksheet (one per student). Write p = m × v and the conservation rule on
the board.
Technology
None. A calculator is helpful but not required.
Student
independence
High. Students work alone, then compare with a partner.
Copies to make
One 2-page worksheet per student
Materials
Pencils, Worksheet, Whiteboard or chalkboard, Calculators (optional)
Goal for today: Students will calculate momentum and impulse and will use conservation of momentum to find
velocities after collisions in one dimension.
Before the bell
☐ Copy the worksheet, one per student (2 pages).
☐ Write on the board: p = m × v (kg·m/s) Impulse = F × t = change in p (N·s)
☐ Also write: In a collision with no outside forces, total momentum before = total momentum after.
☐ Keep the answer key on your desk. You do not need to solve anything yourself.
Say this to start
Good morning! Today’s physics work is about momentum, which is mass times velocity. Heavy and fast objects have a
lot of it. You will calculate momentum, then use the idea that momentum is conserved in a collision. At the end you will
play error detective on a table of collisions. The rules are on the board.
Run of show
Minutes
What you do
What students do
0–5
Take attendance. Hand out the worksheet.
Settle in and take out a pencil.
5–12
Read the board aloud and work this example: a 2 kg cart
moving at 3 m/s has momentum 2 × 3 = 6 kg·m/s. If it
sticks to a 1 kg cart at rest, the 6 kg·m/s is shared by 3 kg,
so the new speed is 6 ÷ 3 = 2 m/s.
Follow the example.
12–28
Tell students to complete Part A (problems 1–5).
Compute momentum and impulse with
units.
28–38
Tell students to do Part B (problems 6–8) and the Error
Detective table. Students write totals in the blank cells of
the table.
Use conservation of momentum, then
check the table rows.
38–45
Tell students to finish questions 9 and 10, then read the
answers from the key aloud.
Finish and mark their work.
45–50
Collect all worksheets in one stack.
Hand in the worksheet.

SubstitutePlans.com
Science · Physics
SP-PHYS-006 · Free to print and use in your classroom · substituteplans.com
Page 3
If things go wrong
• If students ask which direction is positive, tell them to call the starting direction of motion positive.
• If students forget to add the masses in sticking collisions, remind them that the objects move together, so use
the total mass after.
• If students get a negative velocity, explain that it means the object moves in the opposite direction.
• If students finish early, use the early finisher list.
Early finishers
• Write one sentence explaining why a padded dashboard is safer than a hard one, using the word impulse.
• Make up your own sticking collision with an answer of 3 m/s.
Support and challenge
• Support: Have students do problems 1, 2, 4 and 6 and the first two rows of the table.
• Challenge: A 4 kg cart moving at 5 m/s hits a 6 kg cart at rest and they stick. Find the speed after the
collision.
Notes for the teacher (you fill this in)
Jot a few lines before you leave. A full Daily Sub Report is in the free Sub Survival Kit at SubstitutePlans.com.
How far the class got / what to pick up next:
Students who were especially helpful:
Anything the teacher should know: