Warm Ups

Mini Quiz: In PEN w/ no cross outs!

1) At what position is the vertical velocity zero?

2) What is the direction of the acceleration of the rock at point B?a) Upwardb) Downwardc) In the direction of point Cd) In the direction of point A

Mini Quiz: In PEN w/ no cross outs!

A stone is thrown horizontally from the top of a 25.00-m tall cliff. If the stone has a horizontal velocity of 15m/s, how far horizontally from the edge of the cliff will the stone land?

5) What is the first thing you need to calculate to solve this problem?a) Horizontal velocityb) Vertical velocityc) Drop timed) Height of the cliff

3) For an object that is accelerating, the velocity vs. time graph has what type of “shape”

a) Sloped Lineb) Curve c) Flat lined) I don’t know

4) For an object that is accelerating, the position vs time graph has what type of “shape”

a) Sloped Lineb) Curve c) Flat lined) I don’t know

Mini Quiz: In PEN w/ no cross outs!

6) Which of the following v vs. t graphs shows an object moving to rest?

7) Jordon runs at 30m/s. Alicia bikes at 60m/s. If they both travel for 5 seconds, then Alicia will travel:

a)Twice as farb) The same distancec) Four times as fard) Half as far

Av

m/s

(s)0

vm/s

(s)0

vm/s

(s)0

vm/s

(s)0

B C D

Mini Quiz: In PEN w/ no cross outs!

8) Which interval is the object not moving?9) Which interval is the object accelerating?10) Which interval is the object moving backward?a)I -IIb) II-IIIc) III-IVd) IV-V

Mini Quiz: In PEN w/ no cross outs!

11) Which correctly shows the resultant vector of the following two velocities:

a) b) c) d) Zero

12) What is the x component of the following vector:

a) 8.66 b) 51.96N

c) 5.0N d) 29.54N30°

60°

10N

Mini Quiz: In PEN w/ no cross outs!

13) What is the y component of the applied force?

a) 17.2N b) 21.7N

c) 25N d) 12.5N

14) What is the x component of the following vector:

a) 5.0N b) 9.6N

c) 13.0N d) 28.9N

30°

30°

25N

15N

Announcements

Hello Lexa and Johnny (and any other student viewing this). Use this powerpoint to catch up on what you missed!

Forces Introduction

•New Sheet: Lets look at what we know so far…..

•Go through side 1 together•(This is the Forces_Notes 4)…also posted

on my Wiki

Forces WHITEBOARDSFor each of the following questions, determine the net force. You must SHOW YOUR WORK for each question

Y

NET FORCE Vector

X

For the following slides:•1) Find the NET FORCE▫This means you find the sum of the forces acting on

the object. Watch out for the direction. Left = (-) and right = (+). Up = (+), down = (-)

Forces WHITEBOARDS

Forces WHITEBOARDS

Forces WHITEBOARDS

Forces WHITEBOARDS

Forces WHITEBOARDS

Forces WHITEBOARDS

Forces WHITEBOARDS

The following diagrams have forces at an ANGLE

•Forces at an angle have x and y components

•X component = Fcos(θ)•Y component = Fsin(θ)

•Example:•X = 25cos(30)•Y = 25sin(30)

30

25N

Forces WHITEBOARDS

30

30N

15N

Forces WHITEBOARDS

45

50N

45

50N

Forces WHITEBOARDS

30

40N25N

34.64N

Forces WHITEBOARDS

30

20N

20N

Forces IntroductionBut Physics is not just imaginary forces with arrows.....

Often force problems involve real objects, with actual forces acting on them.

We use FREE BODY DIAGRAMS to show these forces

Forces Introduction

WWeight (Gravity): Always directly downward. W = mg

m = mass g = gravity

FN

Normal: A surface pushes perpendicular against an object.

FN is Equal and Opposite of

the sum of all downward forces

Ff

Friction: A force that prevents/goes against (dampens) motion

Will change depending on the surface.

FT

Tension: A PULL in the direction of a rope or a wire

Pulled Object: Value will be given

Hanging: FT is Equal and

Opposite of the sum of all downward forces

FApplied Force: A force can be a push or pull applied to an object

Fx = Fcos( )θ

Fy = Fsin( )θ

* = Angle from the horizontal*θ

Forces IntroductionHow to Solve Equilibrium Problems:

1) Add up the X forces (including x components)

2) Add up the Y forces (including y components)

3) Find the RESULTANT VECTOR.

Forces IntroductionA man pulls a 300kg box at CONSTANT VELOCITY across the floor. He applies a 600N force at an angle of 30°. What is the FRICTION FORCE? Include a magnitude and

direction (left or right).

Free Body:

Forces Introduction: Example 2 (in your notes..1 page)1) A person pulls on a 50 kg desk with a 200N force acting at 30° angle above the horizontal. The desk does not budge.

• a. Determine the value of the frictional force•b. Determine the value of the normal force.