1. 8th Grade Warm ups
9/2 through 9/4

2. Tuesday 9/2 1. Determine the momentum of a ...
a. 60-kg halfback moving eastward at 9 m/s.
b kg car moving northward at 20 m/s.
c. 40-kg freshman moving southward at 2 m/s.

3. ANSWERS 9/2 A. p = m*v = 60 kg*9 m/s p = 540 kg•m/s, east
B. p = m*v = 1000 kg*20 m/s
p = kg•m/s, north
C. p = m*v = 40 kg*2 m/s
p = 80 kg•m/s, south

4. Wednesday 9/3
2. A car possesses units of momentum. What would be the car's new momentum if ...
a. its velocity was doubled.
b. its velocity was tripled.
c. its mass was doubled (by adding more passengers and a greater load)
d. both its velocity was doubled and its mass was doubled.

5. ANSWERS 9/3
A. p = units (doubling the velocity will double the momentum)
B. p = units (tripling the velocity will triple the momentum)
C. p = units (doubling the mass will double the momentum)
D. p = units (doubling the velocity will double the momentum and doubling the mass will also double the momentum; the combined result is that the momentum is doubled twice -quadrupled)

6. THURSDAY 9/4
3. Many people are familiar with the fact that a rifle recoils when fired. This recoil is the result of action-reaction force pairs. A gunpowder explosion creates hot gases that expand outward allowing the rifle to push forward on the bullet. Consistent with Newton's third law of motion, the bullet pushes backwards upon the rifle. The acceleration of the recoiling rifle is ... a. greater than the acceleration of the bullet. b. smaller than the acceleration of the bullet. c. the same size as the acceleration of the bullet.

7. ANSWERS 9/4
Answer: B The force on the rifle equals the force on the bullet. Yet, acceleration depends on both force and mass. The bullet has a greater acceleration due to the fact that it has a smaller mass. Remember: acceleration and mass are inversely proportional.