Lab+Science+Assignments

9/16/2009Chapter 4 p. 72 "Think and Explain" 10, 11, 12, 16-18

10. The heavier cart rolls half as fast as the lighter cart because the heavier cart has more mass when the same amount of force is exerted so that means that the car goes half as fast because it is double the weight. 11.If you push a box at 200N then the friction on the box isn't 200N becuase the 200N is exerted on the crate which means it is not equally and oppositely related to friction. The opposite force against the 200N push is the box pushing back on your hand. 12.If a truck has a head on collision with a sports car both vehicles have the same force but the sports car has more acceleration because it is lighter than the truck. The biggest difference is that the acceleration of the car is a lot higher compared to the acceleration of the truck because the truck has a lot more mass than the car. 16. A.The two forces on the rock is the gravity pushing down to the floor and the floor pushing up against the rock creating a net force of 0. B.The conventional name for the force pushing up against the foot is called the normal force. 17.A. A stone suspended on a string has 2 forces acting on it. One force is the weight of the stone pulling on the string and the other force is the force of the string pulling up on the stone to keep its net force zero. Both forces are equal and opposite. B&C.The vectors should have a zero resultant because it is not moving so all forces must counter balance each other. 18. If the same stone as question 17 is being accelerated up its vectors do not add up to 0. The first force working on the stone is the stone momentum upwards which is greater than the force of gravity and wind resistance combined causing the stone to accelerate, The upward vector is greatest because it has to accelerate upwards.

Multiple Choice 1-10 1.d 2.b 3.b 4.c 5.c 6.a 7.a 8.c 9.a 10.d

9/13/2009 p. 35 "Think and Explain" 2, 4, 9, 13, 19

2.My friend that said " the race car rounded the curve at a constant velocity of 100km/h" is incorrect because velocity is your speed and the speed your changing your direction. He could have said that the race car sped past us at the straight away at a constant velocity of 100km/h.

4.The huge mass of a bear might be threatening but if you run zig zag its mass is to your advantage. This mass is to your advantage because u have a smaller mass which means u can change direction faster and accelerate faster with the force as the bigger bear which needs greater force to change direction and greater force to accelerate.

9. If you are in a car on th highway with a constant velocity of 100km/h, there is a big reason to continue running the engine. You run the engine because the force exerted by the engine pushes the car forward to overcome the force of friction and wind resistance which would other wise decelerate the car, which makes the net force not equal 0 any more.

13. If a man on is standing on a scaffolding in equilibrium and weighs 250 N and the tension on both ropes is 200N the scaffolding must weigh 150 newton because the newtons on the rope in total is 400N and the man weighed 250N which leaves 150N left for the scaffolding.

19. If you toss a coin straight up in a train at constant velocity the coin goes straight back down to its origin if no external force is acting upon it because the coin is moving at the same speed as the train horizontally, and is moving up at the same time which means its moving in unison with the train. If the train does start braking the coin will want to go to in the direction of the front of the train because no external force is working on it but because the train is moving slower than the coin horizontally it will cause the coin to continue moving forward which is faster than the train. If the train was turning and you flipped a coin, the coin will go to one of the sides because the train is turning to the coin while the coin still was going the old direction.

p. 36 "Multiple Choice" 1-10 1.a 2.b 3.c 4.b 5.b 6.c 7.a 8.a 9.d 10.c

p. 55 "Think and Explain" 2, 3, 5, 8, 9, 13, 14 2. When you bang your hand on a wall lightly it doesn't hurt because your hand's inertia isn't very high but if your carrying something heavy it does hurt because your inertia increases so more force is needed to stop your hand when it hits the wall. 3. When a junk car is crushed into a compact cube its mass does not change nor does its weight because it still weighs the same and the mass never change, only the volume changed because everything is compresses so it takes up less space than before. 5. If it takes 1N to push a book at a constant velocity the force of fiction is also one because the net force has to be at 0 for anything to go at a constant velocity. 8.If a basketball full of rocks and a basket ball full of air is dropped from the same height at the same time with the same circumstances then the ball with the rocks will hit first because the ball has more weight so the ball must fall faster so that the air resistance is the same as the weight pulling down to reach terminal velocity compared to the lighter ball which would need less air resistance for the same effect. 9.The forces between a parachutist and her weight going down at terminal velocity is the same because the parachute is only matching the weight of the parachutist as it glides down. 13. The terminal speed of a free falling parachutist is much greater than a parachutist with its parachute open because the air has less surface area to create air resistance so the parachutist must fall faster for the air resistance to equal the parachutist's weight while the surface area of a parachutist and its parachute is a lot greater so the air resistance is reached at a lower speed but the force of the air resistance is still the same. 14.The gravitational pull on the falling body is always the same before, during and after terminal speed because the only force that is changing is the air resistance.

p. 55 "Multiple Choice" 1-10 1.b 2.a 3.b 4.b 5.d 6.c 7.a 8.a 9.d 10.b

8/30/2009 Page 36 Questions 14-16

14. The other scaffold on the right would hold 450N because the 50 N difference on both sides is put on the right side because the man on the left is 50 N lighter than the man on the right.

15. The reading on the scale is half Nellie Newton's weight because of the way she is hanging. One Half of her weight is one side of the rope and the other weight is on the other and the pulley is taking all her weight.

16.The rope doesn't as shown in the left because the most force exerted on one side of the rope is half Harry's weight which is 250 N. The day he tied it to a flagpole he could take his vacation early because the rope was taking all 500 N on one side which caused the rope to snap and Harry to get very injured.

8/27/2009 Page 34 questions 4,6,7

4. What is the name of the property by which objects maintain their state of motion? Inertia is name of the property by which objects maintain their state of motion.

6.Why do we say velocity is a vector quantity and speed is not? Velocity is a vector quantity because it gives direction and speed and speed is not a vector quantity because speed does not give direction.

7.How can you be both at rest and also moving 100,00km/h at the same time? You can be at rest and also be moving 100,000km/h because you are at rest compared to the earth but you are also going 100,000km/h compared to the center of the Galaxy.