1. Bellwork - Work, Energy, Momentum
Physics H
Fall 2009

2. A 300. N fan hangs from the ceiling. What is the fan’s weight
A 300. N fan hangs from the ceiling. What is the fan’s weight? What is the fan’s mass? What is the force of gravity on the fan?
Weight = 300. N
Mass = 30.6 kg
Force of gravity = 300. N

3. 2. A 65 kg runner runs the 1 mile in 6. 5 min. What is his weight
2. A 65 kg runner runs the 1 mile in 6.5 min. What is his weight? What is his mass? What is the force of gravity on the man?
W = 637 N
Mass = 65 kg
Fg = 637 N

4. 3. A 2.5 –g ( kg) bullet traveling at 350 m/s hits a tree and slows uniformly to a stop while penetrating a distance of 12 cm into the tree’s trunk. What force was exerted on the bullet in bringing it to rest? 1276 N ~ 1300 N

5. 4. An ice skater is coasting across a frictionless pond when his little brother teleports into the skater’s arms. What happens to the velocity of the skater? (Ignore any horizontal velocity from his brother)
It decreases due to increased mass

6. 5. Hiker A climbs straight up the hill while Hiker B uses switchbacks.
Who does more work if there is friction?
Switchbacks because of increased distance
Who does more work in the absence of friction?
Same because ending height is the same

7. 6. The rubber band in a toy car can store 75 J of energy
6. The rubber band in a toy car can store 75 J of energy. If the friction force on the car is 10.0 N, how far can the car go? (hint: use energy)
7.5 m

8. 7. A baseball player slides to a stop on level ground
7. A baseball player slides to a stop on level ground. Using energy considerations, calculate the distance the 65.0-kg baseball player slides, given that his initial speed is 6.00 m/s and the force of friction against him is a constant 450 N.
2.6 m

9. 8. A 70. kg skier is pulled 60. m up a 30
8. A 70. kg skier is pulled 60. m up a 30. degree frictionless slope at 2.0 m/s. How much work is done by the motor & What is the power of the motor?
W = J , P = 700 W

10. 9. A 75 kg stunt man falls a total of 25 m onto a foam pad which compresses 1.0 m before he comes to a stop. What is the force from the foam pad?
18375 N ~ 18,000 N

11. 10. a. A student standing on a frozen pond catches a 8 kg medicine ball thrown at 6.0 m/s. How fast is the 70. kg kid going after catching the ball? m/s
b. The catch knocks the kid off his feet and he slides to a stop in 1.5 m. What is the coefficient of friction between the ice and the kid’s jeans? 10. N, .013

12. Warm Up 3/19
Pass over your homework and discuss the following with your partner
How could you calculate the energy stored in the rubber band engine of your car given a ruler, a balance, a ramp with a known height, and a long runway? What information would you need to know/measure?

13. Bellwork #8 10/23
What are some sources of error in the measurements/calculation of the rubber band engine of your car?
To be Collected:
Bellwork
Stampsheet
HW Packet

14. Bellwork
Thinking back to the centripetal force lab, what provided the centripetal force allowing your stopper to travel around in a circle? How would you calculate this force?
If you changed the hanging masses, what were you also changing?

15. Answers:
#2: 7.5 m
#3: 21 kJ, 690 W
#4: 18,000 N
#5: velocity decreases