Exam 1: Chapters 1-4 60% Problems – one problem from WebAssign with different numbers

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Exam 1: Chapters 1-4 60% Problems – one problem from WebAssign with different numbers Understand homework problems Review notes and text Try new problems 40% Multiple Choice Questions Review Power Points (on web page) Review Before Class Assignments Try Questions

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Exam 1: Chapters 1-4

• 60% Problems – one problem from WebAssign with different numbers
• Understand homework problems
• Review notes and text
• Try new problems
• 40% Multiple Choice Questions
• Review Power Points (on web page)
• Review Before Class Assignments
• Try Questions
• Graphs, Pictures and Drawings (Sketches)
• Don’t rely on memorized equations

Chapter 5 The Laws of Motion

5-1a Force – a push or pull.

• CT1: The force of the elevator on Norbert and Zot is
• up.
• down.

Assume the elevator is near the Earth’s surface and that it is right-side up in the cartoon.

• CT2: The force of the non-sticky elevator surface on Norbert and Zot is
• up.
• down.

Assume the elevator is near the Earth’s surface and that it is right-side up in the cartoon.

• CT3: The acceleration of Norbert and Zot is
• up.
• down.
• zero

5-1 B. Mass

The mass of an object is the amount of matter (stuff) in that object. It is the same for a given object everywhere in the Universe. Mass is also called inertia because it resists being moved.

5-2 Newton’s First Law: A body remains in uniform motion (or at rest) unless acted upon by a net external force.

• acceleration due to Earth’s rotation  0.03 m/s2
• acceleration due to Earth’s orbit  0.006 m/s2
• acceleration due to Sun’s orbit  2 x 10-10 m/s2

An inertia frame of reference is a coordinate system (or frame) in which Newton’s Law’s hold.

We will assume that the Earth’s surface is an inertial frame and not make errors greater than 0.03/10 = 0.3%.

A.

B.

C.

D.

E.

CT4

A.

B.

C.

D.

E.

CT5

5-3 Newton’s Second Law: The net external force is equal to the mass times the acceleration.

F = ma

Force and acceleration are vectors

• Fx = max
• Fy = may remember Galileo!
• Fz = maz

Normally we will do problems in a plane with only x and y components.

Calibrating a “Force Meter”

Experiments show forces add as vectors.

Applications of Newton’s Laws - Method

• Draw picture of the problem.
• Choose body (bodies) to isolate.
• Draw Free Body Diagrams (FBDs) for isolated bodies.
• Choose and label coordinate axes.
• Apply Newton’s 2nd Law: Fx = max and Fy = may
• Solve for F, m or a.
• Work out kinematics.
• Check solution is reasonable.

P5.6 (p.136)

Concept Question 6

• P5.6b: If the parachutist comes to rest over a shorter distance, the force exerted by the ground will be
• greater.
• less.
• the same.

FAB

A

B

FBA

5-4 Newton’s Third Law: If body A acts on body B, then body B acts back on body A with a force equal in magnitude but opposite in direction.

FAB and FBA are 3rd Law pairs.

CT7

A.

B.

C.

D.

E.

P5.18

(p.137)

• Concept Question 8
• P5.18b: If the 5 N force is applied to the heavy box instead, the contact force between the boxes will be
• greater.
• less.
• the same.

Orbit of Moon about the Sun

Actual

Exaggerated and incorrect

y

x

5-6 Gravitational Force or Weight

Fg = mg (weight)

g = -9.81 j (m/s2 )

Apparent Weight is the force you actually feel pushing on you – often the floor.

Concept Question 9

• P5.35b: If the constant speed of descent is greater than 1.1 m/s, the force of air resistance is
• greater.
• less.
• the same.

Concept Question 10

• P5.33a: Your normal weight is 610 N and the scale in the elevator reads 720 N. The acceleration of the elevator
• upward.
• downward.
• zero.

Concept Question 11

• P5.33c: Your normal weight is 610 N and the scale in the elevator reads 720 N. The magnitude of the velocity of the elevator is
• increasing.
• decreasing.
• zero.