Newtons laws part 2

9. When you paddle a canoe the canoe goes forward. (Paddle pushed backwards makes canoe go forwards.)

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22. If the acceleration of an object is zero are there any forces acting upon it? Explain.

No!! F = m X a (Newton's 2nd Law) so if a is 0 the force would be 0

1. A frog leaping upward off his lily pad is pulled downward by gravity and lands on another lily pad instead of continuing on in a straight line. (outside force is gravity)

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3. When you are standing up in a subway train, and the train suddenly stops, your body continues to go forward. (You keep moving with the same speed)

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14. What is the force on a 1000 kg elevator that is falling freely? (Hint: Acceleration is due to gravity b/c it's free falling)

1000 kg X 9.8 m/sec2 = 9800 N

4. After you start up your dirt bike, as you give it more gas, it goes faster. (More gas gives it more force therefore it accelerates more)

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5. A pitched baseball goes faster than one that is gently thrown. (Pitching it gives it more force therefore more acceleration - goes faster)

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7. As an ice skater pushes harder with his leg muscles, he begins to move faster. (more force when he pushes harder therefore more acceleration)

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8. When Bobby, age 5, and his dad are skipping pebbles on the pond, the pebbles that Bobby's dad throws go farther and faster than his. (Dad has more mass therefore more force and acceleration)

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15. A force of 20 N acts upon a 5kg block. Calculate the acceleration of the object.

20 N ÷ 5 kg = 4 m/sec2

13. A force of 250 N is applied to an object that accelerates at a rate of 5 m/sec2. What is the mass of the object?

250 N ÷ 5 m/sec2 = 50 kg

2. As the fuel in a rocket ignites, the force of the gas expansion and explosion pushes out the back of the rocket and pushes the rocket forward.

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6. A swimmer pushes water back with her arms, but her body moves forward.

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12. If a 60 kg person on a 15 kg sled is pushed with a force of 300 N, what will be the person's acceleration?

300 N ÷ 75 kg = 4 m/sec2

11. How much force is needed to accelerate a 66kg skier at 2 m/sec2?

66 kg X 2 m/sec2 = 132 N

17. If the person in #16 is on the moon (acceleration due to gravity is 1.622 m/sec2 ), what is their weight?

75 Kg X 1.622 m/sec2 = 121.65 N

16. A 75 kg person has a weight of what on Earth?

75 kg X 9.8 m/sec2 = 735 N

18. If the person in #16 is on the moon, what is their mass?

75 kg because mass doesn't change no matter where you are

19. A man has a weight of 833 N on Earth. What is his mass?

833 N ÷ 9.8 m/sec2 = 85 Kg

20. How are the problems in Part II and Part III similar?

Both formulas are calculating force. One is just for a specific force - weight

25. A passenger sitting in the rear of a bus claims that she was injured as the driver slammed on the brakes, causing a suitcase to come flying toward her from the from the front of the bus. If you were the judge in this case, what disposition would you make? Explain.

I would dismiss the case. Newton's 1st Law says that the suitcase would keep moving forward as the bus stopped. It couldn't have hit someone in the back of the bus.

24. A space explorer is moving through space far from any star or planet. She notices a large rock floating around the cabin of her ship. Should she push it gently or kick it toward the storage compartment? Why?

It depends on the size of the rock. F = ma. (Newton's 2nd Law) In order to change the acceleration of the rock, you apply a force. The force you apply depends on the mass of the rock

21. When a golf ball is dropped to the pavement, it bounces back up. Is a force needed to make it bounce up - use one of Newton's Laws to explain your answer.

No! Newton's 3rd Law tells us that when the 2 collide (the ball and the pavement) there is an equal and opposite force exerted on the golf ball so it bounces back up.

23. If gold were sold by weight would you rather buy it in Denver or Death Valley? If it were sold by mass, in which of the two locations would you prefer to buy it and why?

Weight depends on gravity. (Newton's 2nd Law: Fw = m X g)Gravity is stronger closer to the source (the center of the earth). In Death Valley, gravity is higher so cost of gold would be higher. You would want to buy your gold in Denver (in the mountains). Mass doesn't change no matter where you are so you could buy the gold anywhere if it were sold by mass.

The amount of _________needed to make an object change its ______ depends on the ___ of the object.

force; acceleration; mass

When 1 object exerts a ____ on a 2nd object, the 2nd object exerts an _________ and _______ force back on the 1st object.

force; equal; opposite

An object at __ stays at ____________ and an object in _______ keeps moving with the same _______ unless an ________ force acts on it.

rest; rest; motion; velocity; outside