DAY 54

Goals: SWBAT...

1. Answer the following question: Momentum - how can you prove it is conserved?

Warm-Up (5min):

1. When considering an isolated system, both before and after a collision, how could you tell if momentum is conserved?

2. Is momentum conserved or not conserved in each of the following scenarios? Support your answer with math

CLASSWORK

1. #054A: Solving Explosion Momentum Problems

• Since total system momentum is conserved in an explosion occurring in an isolated system, momentum principles can be used to make predictions about the resulting velocity of an object. Problem solving for explosion situations is a common part of most high school physics experiences. Consider for instance the following problem:
  • A 56.2-gram tennis ball is loaded into a 1.27-kg homemade cannon. The cannon is at rest when it is ignited. Immediately after the impulse of the explosion, a timer measures the cannon to recoil backwards a distance of 6.1 cm in 0.0218 seconds. Determine the post-explosion speed of the cannon and of the tennis ball.

• Step 1: List the given info (hint, there are four givens). Are there any unit changes necessary? (yes, so make that change). Organize given info and problem into "BEFORE" and "AFTER" parts
• Step 2: Unknown, equation
• Step 3: rearrange, Substitute, Solve BEFORE and AFTER parts of problem

2. #054B: Practice Problems:

1. Two soda cans are at rest on a stand. A firecracker is placed between the cans and lit. The firecracker explodes and exerts equal and opposite forces on the two cans. Assuming the system of two cans to be isolated, the post-explosion momentum of the system ____.

a. is dependent upon the mass and velocities of the two cans

b. is dependent upon the velocities of the two cans (but not their mass)

c. is typically a very large value

d. can be a positive, negative or zero value

e. is definitely zero

2. Students of varying mass are placed on large carts and deliver impulses to each other's carts, thus changing their momenta. In some cases, the carts are loaded with equal mass; in other cases they are unequal. In some cases, the students push off each other; in other cases, only one team does the pushing. For each situation, list the letter of the team that ends up with the greatest momentum. If they have the same momentum, then do not list a letter for that situation. Enter the four letters (or three or two or ...) in alphabetical order.

3. Two ice dancers are at rest on the ice, facing each other with their hands together. They push off on each other in order to set each other in motion. The subsequent momentum change (magnitude only) of the two skaters will be ____.

a. greatest for the skater who is pushed upon with the greatest force

b. greatest for the skater who pushes with the greatest force

c. the same for each skater

d. greatest for the skater with the most mass

e. greatest for the skater with the least mass

4. A 62.1-kg male ice skater is facing a 42.8-kg female ice skater. They are at rest on the ice. They push off each other and move in opposite directions. The female skater moves backwards with a speed of 6.22 m/s. Determine the post-impulse speed of the male skater.

5. A 1.5-kg cannon is mounted on top of a 2.0-kg cart and loaded with a 105.4-gram ball. The cannon, cart, and ball are moving forward with a speed of 1.27 m/s. The cannon is ignited and launches the ball forward with a speed of 75 m/s. Determine the post-explosion velocity of the cart.

3. #053: Extra Credit Presentations

At Home Learning (HW)

1. Complete the classwork from #054B