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2016 Chapter 5 Newton’s Laws!!! Very Important!!

Force and Motion IHope you find balance in this world of constant motion!

1. What is Newton’s 1st law?

a. What are the possible motions for an object with NO NET FORCE acting on it?

b. What are the three possibilities for the motion of an object that accelerates (has a net force)?

2. You are a passenger in a car and not wearing your seat belt. Without increasing or decreasing its speed, the car makes a sharp left turn, and you find yourself colliding with the right-hand door. Which is the correct analysis of the situation?

a. Before and after the collision, there is a rightward force pushing you into the doorb. Starting at the time of collision, the door exerts a leftward force on you.c. Both of the aboved. Neither of the above

3. What does the word equilibrium mean?

4. Several forces act on an object, but the object is in equilibrium. Which of the following statements about the object must be true?I. It has zero accelerationII. The net force acting on it is zero.III. It is at rest.IV. It is moving with constant velocity.(A) I and II(B) I and III(C) I and IV(D)II and III(E) II and IV

5. What is Newton’s 2nd law?

Be able to apply Newton’s 1st Law .

Know the difference between mass and weight


Mass versus Weight

Analyze situations in which a particle remains at rest or moves with constant velocity

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6. Astronauts on the Moon can jump so high because


b. Their mass is less than it is on Earth

c. There is no atmosphere on the moon

Force versus Net Force7. An object of mass 100 kg is initially at rest on a horizontal frictionless surface. At time t=0,

a horizontal force of 10 N is applied to the object for 1 sec and then removed. Which of the following is true of the object at time t=2 s if it is still on the surface?

a. It is at the same position it had at t=0, since a force of 10N is not large enough to move such a massive object

b. It is moving with constant nonzero accelerationc. It is moving with decreasing accelerationd. It is moving at a constant speede. It has come to rest some distance away from the position it had at t=0

8. An elevator cab that weighs 27.8kN moves upward. What is the tension in the cable if the cab’s speed is

a. Increasing at a rate of 1.22 m/s2

NET force produces acceleration


b. Decreasing at a rate of 1.22 m/s2

9. The picture shows an overhead view of a 0.025 kg lemon half and two of three horizontal forces that act on it as it is on a frictionless table. Force F1 has a magnitude of 6 N at 150 degrees, Force F2 has a magnitude of 7 N and is at 300 degrees. In unit vector notation what is the third force if the lemon half

a. Is stationary( (equilibrium!)

b. Has constant velocity v=(13i-14j) m/s (also equilibrium!)

c. Has varying velocity v= (13ti-14tj) m/s, where t is time

10. Only two forces act on a 3 kg object that moves with an acceleration of 3m/s2 in the positive y direction. If one of the forces acts in the positive x direction and has a magnitude of 8 N, what is the magnitude of the other force?

11. Is the normal force on a body always equal to its weight?

12. A block with weight of 3N is at rest on a horizontal surface. A 1N upward force is applied to the block by means of an attached vertical string. What are the magnitude and direction of the force of the block on the horizontal surface?

Use unit Vector notation to add forces

Normal force is a balancing force!


13. Problem solving strategy

14. A person pulls a block across a rough horizontal surface at a constant speed by applying a force F. The arrows in the diagram below correctly indicate the directions, but not necessarily the magnitudes of the various forces on the block. Which of the following relations among the force magnitudes W,f,N, and F must be true?

a. F=f and N=Wb. F=f and N>Wc. F>f and N<Wd. F<f and N=We. None of the above choices

15. Consider a person standing in an elevator that is accelerating upward. The upward normal force N exerted by the elevator floor on the person is_______ The downward weight W of the person

a. Larger thanb. Identical toc. Smaller than

16. A 50 kg passenger rides in an elevator cab that starts from rest on the ground floor of a building at t=0 and rises to the top floor during a 10 s interval. The cab's acceleration as a function of the time is shown above, where positive values of the acceleration mean that it is directed upward.

What are the (a) magnitude and (b) direction (up or down) of the maximum force on the passenger from the floor,

W

FN

f


What are the (c) magnitude and (d) direction of the minimum force on the passenger from the floor,

What are the (e) magnitude and (f) direction of the maximum force on the floor from the passenger

17. Draw a freebody diagram and a reference frame for each of the following situationa. Arlo on an elevator b. Alice pulling a block on a horizontal surface

c. A car on an inclined plane d. A block being pulled up an inclined plane

e.. An Atwood f. a modified Atwood

Draw a well labeled, freebody diagram showing all real forces that act on the object

Write vector equation that results from Newton’s 2nd Law


g. A monkey climbing a rope that is over a limb and has a block attached to the other end.

18. A small box is on a ramp tilted at an angle above the horizontal. The box may be subject to the following forces: friction (f),

gravitational (mg), pulling or pushing (Fp) and normal (N). In the following free-body diagrams for the box, the lengths of the vectors are proportional to the magnitudes of the forces.

a. Which figure best represents the freebody diagram for the box if it is accelerating up the ramp?

b. Which figure best represents the freebody diagram for the box if it is at rest on the ramp?

c. Which figure best represents the freebody diagram for the box if it is sliding down the ramp at constant speed?

19. A block of mass m is projected up from the bottom of an inclined ramp with an initial velocity vo. The ramp has negligible friction and makes an angle θ with the horizontal. A motion sensor aimed down the ramp is mounted at the top of the incline so that the positive direction is down the ramp. The block starts a distance D from the motion sensor, as shown


above. The block slides partway up the ramp, stops before reaching the sensor, and then slides back down.

a. Consider the motion of the block at some time t after it has been projected up the ramp. Express your answers in terms of m, D, vo, t, θ and physical constants, as appropriate.

i. Determine the acceleration a of the block

ii. Determine an expression for the velocity v of the block

b. On the axes provided below, sketch graphs of position x, velocity v, and acceleration a as functions of time t for the motion of the block while it goes up and back down the ramp. Explicitly label any intercepts, asymptotes, maxima, or minima with numerical values or algebraic expressions, as appropriate.

20. Newton’s 3rd LawIf F1 is the magnitude of the force exerted by the Earth on a satellite in orbit about the Earth and F2 is the magnitude of the force exerted by the satellite on the Earth, then which of the following is true?

a. F1 is much greater than F2

b. F1 is slightly greater than F2

c. F1 is equal to F2

d. F2 is slightly greater than F1

e. F2 is much greater than F1

21. Consider a horse pulling a buggy. Is the following statement true?The weight of the horse and the normal force exerted by the ground on the horse constitute and interaction pair that are always equal and opposite according to Newton’s third law?


22. A 40 kg girl and an 8.4 kg sled are on the frictionless ice of a frozen lake, 15 m apart but connected by a rope of negligible mass. The girl exerts a horizontal 5.2 N force on the rope.

a. What is the acceleration of the sled?

b. What is the acceleration of the girl?

c. How far from the girl’s initial position do they meet?

23. Each of the figures to the right shows a tractor attached to an object. The tractor exerts the same force on each object. Which of the following is a true statement about an object and the relative magnitude of the force exerted by the object on the tractor?

a. The magnitude of the force exerted by the truck on the tractor is greatest, because the resulting motion is the direction opposite the tractor’s pull

Newton’s 3rd Law is an equal and opposite force on TWO objects!

Understand Newton’s 3rd law so you can identify the force pair and the magnitude and direction of each force

Know the difference between Newton’s 2nd Law and Newton’s 3rd Law.


b. The magnitude of the force exerted by each object on the tractor is equal, because the tractor exerts an equal force on each object

c. The magnitude of the force exerted by the boulder on the tractor is the least, because no motion results.

d. The magnitude of the force exerted by the wagon on the tractor is least, because the resulting motion is in the direction of the tractor’s pull.

24. Consider a car at rest. We can conclude that the downward gravitational pull of Earth on the car and the upward contact force of Earth on it are equal and opposite because.

a. The two forces form an interaction pairb. The net force on the car is zeroc. Neither of the above

25. Rank these arrangements, from greatest to least, on the basis of tension in the rope R.

26. If Arlo pulls two blocks with a force of 20N, what is the force pulling the 3 kg block?

27. The figure above shows a train of four blocks being pulled across a frictionless floor by force F. What total mass is accelerated to the right by

3kg2kg

10kg 3kg 5kg 2kgCord 1 Cord 2 Cord 3

Newton’s 2nd and 3rd Laws applied to tension between boxes.

R RR R

R RR R

20N 35N 80N120N80N

45N

40N

40N 40N

40N40N 40N

60N80N 80N

AB

C D

E F G H


a. forceF

a. cord 3

b. cord 1

c. Rank the blocks according to their accelerations, greatest first

d. Rank the cords according to their tension, greatest first

28. Three blocks A,B, and C, each have mass M and are connected by massless strings as shown above. Block C is pulled to the right by a force F causing the entire three-block system to accelerate. Assuming frictionless contact between the blocks and the level table beneath them, what is the net force experienced by block B?

a. 0b. F/3c. F/2d. 2F/3e. F

29. The picture above shows four penguins that are being playfully pulled along very slippery (frictionless) ice by a curator (Rachael of course). The masses of the three penguins and the tension in two of the cords are m1=12 kg, m3=15 kg, m4= 20 kg, T2 =111 N, and T4 = 222 N. Find the penguin mass m2 that is not given.

A B CM M M F


30. An Atwood has a block of mass 5 kg and a block of mass 3 kg. a. What is the acceleration of the system when released from rest?

b. What is the tension in the rope?

c. If the 5 kg block travels 3 meters until it strikes the floor, how fast is it traveling when it strikes the floor?


31. A math book and a physics book are tied together with a length of string. With the string taut, one book is pushed off the edge of a table. As it falls, the other book is dragged horizontally across the table surface. With no friction, acceleration of the books is

A. zero.B. g/2.C. g.D. a value between zero and g.E. a value that could be greater than g.

32. A block of mass M /2 rests on a frictionless horizontal table, as shown above. It is connected to one end of a string that passes over a massless pulley and has another block of mass M /2 hanging from its other end. The apparatus is released from rest.(a) Derive an expression for the speed vh of the hanging block

as a function of the distance d it descends.

Now the block and pulley system is replaced by a uniform rope of length L and mass M, with one end of the rope hanging slightly over the edge of the frictionless table. The rope is released from rest, and at some time later there is a length y of rope hanging over the edge, as shown below. Express your answers to parts (b), (c), and (d) in terms of y, L, M, and fundamental constants.

(b) Determine an expression for the force of gravity on the hanging part of the rope as a function of y.

Analyze motion given massless pulley, which means constant tension

Be able to determine time or distance or final velocity given acceleration due to NET force


33. A block of mass m1=3.70 kg on a frictionless inclined plane of angle 30.00 is connected by a cord over a massless, frictionless pulley to a second block of mass m2=2.30 kg hanging

vertically.a. What is the magnitude of the acceleration of each block?

b. What is the direction of the acceleration of the hanging block?

c. What is the tension in the cord?

34. A 1 kg tin of antioxidants on a frictionless inclined surface is connected to a 2kg tin of corned beef. The pulley is massless and frictionless. An upward force of 6 N acts on the corned beef tin, which has a downward acceleration of 5.5m/s2. What is the tension in the connecting cord?

Be able to recognize if there is a varying force and what that means for acceleration and stopping distance

Determine time/distance/final velocity using acceleration


35. A man sitting in a bosun’s chair that dangles from a massless rope, which runs over a massless, frictionless pulley and back down to the man’s hand. The combined mass of man and chair is 95.0 kg.

a. With what force magnitude must the man pull on if he is to rise with a constant velocity?

b. With an upward acceleration of 1.30 m/s2?

36. Alice pushes two boxes of 10 kg and 5 kg with a force of 20 N.

a. Draw a free-body diagram for each of the blocks.

Solve Bosun’s chair problems

Apply Newton’s 3rd

law in analyzing the force of contact

Solve problems with boxes on incline planes


b. What is the acceleration of the blocks?

c. Find the force of contact between the two blocks.

37. Two blocks are in contact on a frictionless table. A horizontal force is applied to the larger block, as shown in the picture.

a. If m1=2.3 kg, m2=1.2 kg, and F=3.2 N, find the magnitude of the force between the two blocks.

b. Show that if a force of the same magnitude F is applied to the smaller block but in the opposite direction, the magnitude of the force between the blocks is 2.1 N, which is not the same value calculated in (a).

20 N3 kg 2 kg


38. Two blocks are pushed along a horizontal frictionless surface by a force of 20 newtons to the right, as shown above. The force that the 2 kilogram block exerts on the 3 kilogram block is.

a. 8 newtons to the leftb. 8 newtons to the rightc. 10 newtons to the leftd. 12 newtons to the righte. 20 newtons to the left

39. In the picture, a chain consisting of five links, each of mass 0.100 kg, is lifted vertically with constant acceleration of magnitude a =2.50 m/s2. Find the magnitudes of

a. the force on link 1 from link 2

b. the force on link 2 from link 3,

c. The force on link 3 from link 4,

d. the force on link 4 from link 5.

e. find the magnitude of the force F on the top link from the person lifting the chain


f. the net force accelerating each link.

web viewwhat are the possible motions for an object with no net force ... force f. 1 has a magnitude...

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