Homework

Class Work, Thursday September 10, 2009
2. The race car driver rounded the curve at a constant velocity of 100 km/h is wrong because velocity is the same speed and direction of an object. If the car is going around a corner, it is not going in the same direction, so it is not the same velocity.

4. If a huge bear was chasing me and I ran in a zigzag pattern, the bear's mass would work to my advantage because the bear would have to change its velocity every couple of seconds and the bear would not be able to do this for a long period of time, thus, letting me escape.

9. When a car moves along the highway at a constant velocity, the net force on it is zero. You have to have to keep your motor running, because you have to keep the constant velocity to have the net force of zero on it.

13. The weight of the scaffold is 150N, because 250N plus 150N is 400N, which is the whole weight of the scaffold and the man.

19. If you toss a coin straight upward while riding on the train, the coin lands right back in your hand when the train is going along a straight-line track. This is because of the inertia and it keeps the coin with you. Same thing happens when the train is turning. When the train slows down, the coin flies forward, because the inertia of the coin is moving forward.

1. A 2. B 3. C 4. B 5. D 6. C 7. A 8. A 9. D 10. C

2. It hurts to bang against a wall when your carrying a heavy load because the heavy load makes you hit the wall harder, causing more pain. Newton’s Firsr law is most applicable here.

3. When a car is crushed into a compact cube, the mass and weight stay the same because all you do is make it smaller, you don't take any parts away from it. The volume changes because its from a big car to a smaller and easier to move cube.

5. The force of the friction would be 1N, because every action has an opposite reaction.

8. The basketball filled with the rocks would accelerate faster because of the formula a = F/m. The mass of the ball filled with rocks is greater, so it accelerates faster.

9. The force of gravity is stronger than the air resistance, because you slowly drift down, instead of staying in the same place.

13. The terminal speed of the parachutist before opening the parachute is much greater than the terminal speed when the parachute is out. This is because the surface area increases.

14. The gravitational force on a falling body before it reaches terminal velocity is less than when the body reaches the terminal velocity.

1. A 2. C 3. B 4. B 5. D 6. A 7. A 8. A 9. A 10. B

Thursday, September 3rd 2009
The heavier our car is, the more inertia it has and the more friction it has. With more friction and inertia, the motor needs to be more powerful to move the car. This is why a lot of the cars don't move very fast, because the motor is struggling to fight against inertia and friction.

Tuesday, September 1st 2009
We can estimate our car's acceleration by using the data we collected because we can use the acceleration formula. We find out the change of velocity and how long it took to cover the one meter, divide, and then we have the acceleration.

Monday, August 31st 2009
Page 36: # 14-16

14) The reading on the right scale would be 350 N. This is because the upward tension is equal to the sum of the scaffold plus the two painters. This makes the net force of the scaffold zero, giving it the name mechanical equilibrium.

15) The readings of the scale should be half her original weight. Meaning that if you multiply the scales' reading by two, you get Nellie's weight. This method works because of the downward force of Nellie's weight, and the tension from both strings to hold her up.

16) The rope doesn't break because his original weight is divided by two, because there are two ropes that hold him. His weight divided by two is 250 N, which is under 300 N, so the rope doesn't break. But when he tied his rope to the flag pole, the rope had to hold his 500 N weight, not the usual 250 N, this caused the rope to break, Harry to fall into an early vacation.

Sunday, August 30th 2009
Page 35: #4,6 and 7

4) If a huge bear was chasing me and I ran in a zigzag pattern, the bear's mass would work to my advantage because the bear would have to change its velocity every couple of seconds and the bear would not be able to do this for a long period of time, thus, letting me escape.

6) If a ball is at rest in the middle of a toy wagon and when the wagon is pulled forward, the ball rolls against the back of the wagon. This is explained by Newton's first law because the balls inertia tries to keep the ball in one place, but because the wagon is moving forward, the ball rolls to the back of the wagon.

7) You lurch forward in a bus that suddenly slows because your inertia is moving forward, and when the bus stops, your inertia tries to keep moving forwards. You lurch backwards when the bus suddenly picks up speed because your inertia is where you were sitting still, and when the bus lurched forward, and went backwards. This is an example of Newton's first law.