1-14-09

Today I walked into another delightful physics class with Mr. Manning. A smiling Mr. Manning greeted me at the door. After being sick for a day I felt a withdraw from my ever extending knowledge of the great world of physics. He then gave us our daily questions..

The Daily Questions were- Who has a mass of 60 kg and stands at rest on ice, catches a 20 kg ball that is thrown to him at 10 km/h. How fast does Jocko and the ball move across the ice?

Answer: Mass is 20 kg multiplied by 10 kg equals 200+ the momentum of Jocko which is 0 80 is the mass of Jocko (60) + 20 of the ball 200=80 v with arrow over (2.5 km/h = v with arrow over it)

Question: Strictly speaking, when a gun is fired, compared with momentum of the recoiling gun, the opposite momentum of the bullet is … A) Less B) More C) The same

The answer: Less Take into account the gas from the chamber coming out of the gun, a little explosion takes place inside the gun and the gunpowder and gases escape on release Add the powder gases and the bullet equals

Question: An ice sail craft is stalled on a frozen Lake on a windless day. A large fan blows air into the sail. If all the wind produced by the fan strikes and bounces backward from the sail, the craft will move

A to the left –backwards B to the right- forward C not at all

Student answer: Wind bounces back it will propel the boat because it won’t be in the system anymore.

The answer: B The larger impulse is taking place at the sail, because the change in the velocity of the wind is greater there then at the fan. The wind brings it up to a positive velocity and then the sail turns it into negative velocity

Mr. Manning then gave us a worksheet titled: Conservation of Momentum Practice Problems: Physics 1. These are the directions: In each case, you can find the total momentum (either before or after the interaction), then determine the missing momentum and velocity Or You can use the Conservation of Momentum equation directly to solve for your unknown.

These questions gave me great difficult until my dear friend Ben Singer drew a diagram to help me place the numbers in a picture which made the problems easier to solve.

The question:

2. Jorge, who has a mass of 50 kg and stands at rest on ice, catches a 10 kg ball that is thrown to him at 5 m/s. How fast does Jorge and the ball move across the ice?

The answer: Jorge’s mass is 50 kg and he is at 0 m/s Multiplying those together gets the product of 0 The mass of the ball is 10 kg and it is thrown at 5 m/s Multiply those together and the product is 50 Add the two products and get the sum of 50 To find how fast Jorge and the ball are moving across the ice take the total force of 50 and divide it by the combined mass of the ball (10 kg) and Jorge (50) ; which is 60 And get 0.83 m/s as the answer

After we went over the answers and talked about what would be on our test I am so excited to take tomorrow!