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**ToC, Ch 4**|

**Ch 5, Newton"s 3rd Law**|

**Exercises (Discussion Questions)**

**Ex 4.* prior to the time of Galileo and also Newton, that was assumed by plenty of learned scholars the a rock dropped from the optimal of a tall mast the a moving ship would fall vertically and hit the deck behind the mast by a distance equal come how much the ship had moved front while the stone was falling. In light of your understanding of Newton"s Laws, what perform you think around this?**

As we have actually seen on **The mechanical Video**, and also as I have tried to demonstrate in walking back and soon in former of the classroom while throwing a ball, the ball or stone should fall and also hit the deck at the base of the mast.

You are watching: An apple weighs 1 n. when the apple is held at rest above your head, the net force on the apple is

**Ex 4.2 deserve to the velocity of an item reverse direction if mintaining a consistent acceleration? If so, offer an example; if not, define why.**

Yes, as displayed in the sketch here. Take into consideration a block relocating to the ideal with one acceleration to the **left** as shown here. The block will eventually involved rest through v = 0. If the acceleration **stays the same,** the block will certainly now move to the **left** and also continue to rise its speed. Throughout the sketch presented here, the acceleration is consistent and **to the left**.

**Ex 4.3 If an object is no accelerating, deserve to you conclude the no force acts upon it?**

You can conclude the there is **no net force** on the object. There might be plenty of separate pressures acting on it, but their **sum** is zero!

**Ex 4.5 If the takes 1 N to push horizontally ~ above your book to make it on slide at constant velocity, just how much force of friction acts on the book?**

Horizontally, her 1 N force acts come the right while the friction force acts come the left. If the book slides at **constant** **velocity** that method it moves through **zero acceleration** therefore the **net force**must be **zero.** Therefore, the friction force is additionally **1 N.**

**Ex 4.6 Is it feasible to go approximately a curve in the lack of a force?**

No, going about a curve way the **velocity changes** direction. Any readjust in velocity requires an acceleration. And also any acceleration needs a (net) force.

Think of what happens during the winter when there may be ice cream on a curve so the the pressure of friction in between tires and also road is an extremely small. Then cars have the right to not go roughly such a curve and also end increase in a ditch.

**Ex 4.9 A 400-kg be afflicted with grasping a vertical tree slides under an consistent velocity. What is the friction force that acts on the bear?**** The bear who mass is 400 kg has a downward weight that 4,000 N since**

**W = m g = (400 kg)(10 m/s2) = 4,000 N**

**Since the bear slides under at continuous velocity (or zero acceleration!), the net force on the bear have to be zero. The net pressure is the sum of the downward weight and the upward friction force. These two must add to zero. So the friction force is likewise 4,000N.**

**Ex 4.11 In the orbiting space shuttle you room handed two the same boxes, one filled v sand and also the various other filled with feathers. How deserve to you tell which is which without opening the boxes?**

**Shake the boxes earlier and forth or up and down and see i m sorry is easier to accelerate.**

**Ex 4.17 What happens to her weight when your mass increases?**

**Since weight is proportional come mass, or W = m g, any type of increase in mass corresponds to a proportional increase in weight.**

**Ex 4.18 What is your very own mass in kilograms? her weight in newtons?**

Recall that the a mass of 1 kg has a weight of 2.2 lbs. To uncover mass in kilograms, take her weight in lbs and also **divide by 2.2** (this method a load of 2.2 lbs coincides to a mass of 1.0 kg or a weight of 22 lbs synchronizes to a massive of 10 kg or a weight of 220 lbs coincides to a fixed of 100 kg.)

Recall that the load of 1 kg is 9.8 newtons. To discover your **weight** in newtons, take your **mass** in kilograms and **multiply through 9.8** .

Here is a brief table:

weight (in pounds) | fixed (in kilograms) | load (in newtons) |

100 | 45.5 | 446 |

125 | 56.8 | 557 |

150 | 68.2 | 668 |

175 | 79.5 | 779 |

200 | 90.9 | 891 |

225 | 102.3 | 1,003 |

**Ex 4.19 A rocket becomes progressively easier to accelerate as it travels v space. Why is this so?**

The force of the rocket enging -- referred to as the **thrust** -- stays constant. But the **mass** the the rocket decreases as it provides its fuel. As this continuous forces continues to act on a smaller and smaller mass, the **acceleration increases.**

**Ex 4.29 as soon as you run vertically off the ground, what is your acceleration after ~ you reach your greatest point?**

Once her feet leave the ground, you"re in **free fall**. Once your feet leave the ground, the **only force** acting on girlfriend is the **force that gravity, her weight**. As soon as your feet leaving the ground, your acceleration is the acceleration that gravity, **downward in ~ 9.8 m/s2.**

**Ex 4.32 A friend claims that as long as a car is at rest, no pressures act on it. What execute you speak if you"re in the the atmosphere to correct this statement?**** because that a car -- or any object -- at rest, the net force is zero. But having the net force to it is in zero is not the exact same things as having no forces exhilaration on the vehicle at all!**

**Ex 4.35 What is the net force on a 1 N apple when you organize it at rest over your head? What is the net pressure on the after you release it?**

If you"re hold the apple at rest, the **net force** ~ above the apologize is **zero.**

Once friend drop the apple, the only pressure on it is its weight of 1 N

**Ex 4.43 how does the terminal speed of a parachutist before opening a parachute compare to terminal speed after? Why is there a difference?**

**Ex 4.44 exactly how does the gravitational force on a falling human body compare through the wait resistance that encounters before it will terminal velocity? After?**

**Ex 4. 31 What is the net force on one apple that weighs 1 N once you organize it at rest over the floor? What is the net pressure on it when you relax it?**

For **anything** at rest, the **net force** is zero.

When you relax the apple, the **only** force on the is the pressure of gravity, which we speak to the **weight** of the apple, and we are told the that is **one Newton.**

**Ex 4.44 exactly how does the load of a falling body compare to the waiting resistance the encounters just prior to it get terminal velocity? After?**

Before getting to terminal velocity, the falling body is tho accelerating, so its weight (the force of gravity) is still better than the force because of air resistance.

See more: Words That Start With Tens ', Words Created Using The Letters In 'Tens'

After reaching terminal velocity, the fallout’s body drops with constant speed therefore the net pressure on it have to be zero. This way the pressure of heaviness (its weight) acting **downward** is simply **balanced** through the force of waiting resistance exhilaration **upward**.** **

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**ToC, Ch 4**|

**Ch 5, Newton"s 3rd Law**|

**Pb 4.4 If a mass of 1 kg is sped up 1 m/s2 by a pressure of 1 N, what would be the acceleration the 2 kg action on by a pressure of 2 N?**

Use Newton"s second Law,

F = m a2 = 2 x ?

2 = 2 x a

a = 1

a = 1 m/s2

**Pb 4.5 just how much acceleration go a 747 jumbo jet of mass 30 000 kg experience in takeoff when the thrust of every of four engines is 30 000 N (for a complete thrust the 120 000 N)?**

Again, use Newton"s second Law,

F = m a120 000 = (30 000) a

a = 4

a = 4 m/s2

**Pb 4.7 A firefighter of mass 80 kg slides under a vertical pole through an acceleration of 4 m/s2. What frictional pressure does the pole exert on her?**

First, we can discover the **net force**, for that is always the F that appears in Newton"s second Law,

Fnet = (80 kg) (4 m/s2)

Fnet = 320 N

What forces consist of this net pressure Fnet? heaviness pulls **down** with the firefighter"s weight,

w = (80 kg) (10 m/sw)

w = 800 N

Then over there is the **force that friction**, Ff, which opposes the firefighter"s motion. So the pressure of friction Ff must point **up**. The **net force** Fnet is consisted of of these two forces,

320 N = 800 N - Ff

320 N = 800 N - 480 N

Ff = 480 N

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**ToC, Ch 4**|

**Ch 5, Newton"s 3rd Law**|

**Typical multiple-guess questions:**

1. Massive is a measure up of

**a) the volume of an item**

b) the dimension of one object

c) how an overwhelming it is to change the movement of an object

d) the velocity of one object

2. The weight of an object is

a) the same thing as the mass of an itemb) the amount of every the pressures on an object

c) the force of heaviness on one object

d) always less than the mass, also in a vacuum

3. The net pressure on a 1-kg object, in ~ rest, is

a) 9.8 Nb) 4.9 N

c) 1.00 N

d) zero

4. The net pressure on a 1-kg object, in free fallt, is

a) 9.8 Nb) 4.9 N

c) 1.00 N

d) zero

5. A pressure of 24 N acts upon an object who mass is 6 kg. This reasons the thing to accelerate at

a) 2 m/s2b) 4 m/s2

c) 6 m/s2

d) 10 m/s2

6. A car, through mass that 1,000 kg, speeds up at 2 m/s2. The net pressure exerted on the auto must be

a) 500 Nb) 1,000 N

c) 2,000 N

d) 10,000 N

7. The load of a 1,000-kg auto is

a) 500 Nb) 1,000 N

c) 2,000 N

d) 10,000 N

8. A fireman, whose load is 500 N, slides under a pole with an acceleration that 3 m/s2. The forces that act on him are his weight pulling him down and also the force of friction pulling increase on him to slow-moving him down. The pressure of friction should be

a) 90 Nb) 150 N

c) 350 N

d) 500 N

** answers to usual multiple-guess questions:**

1. Mass is a measure up of

**a) the volume of an item**

b) the dimension of an object

**c) how daunting it is to adjust the activity of an object**

d) the velocity of an object

2. The weight of an item is

**a) the exact same thing as the mass of things**

b) the amount of all the forces on an object

**c) the pressure of heaviness on an object**

d) constantly less than the mass, also in a vacuum

3. The net pressure on a 1-kg object, in ~ rest, is

**a) 9.8 N**

b) 4.9 N

c) 1.00 N

**d) zero**

4. The net pressure on a 1-kg object, in cost-free fallt, is

**a) 9.8 N**

b) 4.9 N

c) 1.00 N

d) zero

5. A pressure of 24 N acts upon an object who mass is 6 kg. This reasons the object to advice at

**a) 2 m/s2**

**b) 4 m/s2**

c) 6 m/s2

d) 10 m/s2

F = m a24 N = ( 6 kg ) ( a )

24 N = ( 6 kg ) ( 4 m/s2)

a = 4 m/s2

6. A car, through mass that 1,000 kg, speeds up at 2 m/s2. The net force exerted ~ above the car must be

**a) 500 N**

b) 1,000 N

**c) 2,000 N**

d) 10,000 N

7. The weight of a 1,000-kg vehicle is

**a) 500 N**

b) 1,000 N

c) 2,000 N

**d) 10,000 N**

w = (1,000 kg) (10 m/s2)

w = 10,000 N

8. A fireman, whose weight is 500 N, slides down a pole v an acceleration the 3 m/s2. The forces that act on him space his weight pulling him down and also the force of friction pulling up on that to sluggish him down. The force of friction must be

**a) 90 N**

b) 150 N

**c) 350 N**

d) 500 N

F = maFnet = ma

Fnet = Fgravity - Ffrict

Fgravity = w = m g

500 N = m (10 m/s2)

m = 50 kg

Fnet = ma = (50 kg) (3 m/s2)

Fnet = 150 (kg m/s2)

Fnet = 150 N

Fnet = Fgravity - Ffrict

150 N = 500 N - Ffrict

Ffrict = 500 N - 150 N = 350 N

**Ffrict = 350 N**

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**ToC, Ch 4**|

**Ch 5, Newton"s third Law**|

an introduction back to "Table that Contents" ToC, Ch5, Netwon"s third Law (C) 2003, Doug Davis; all civil liberties reserved