Physics 101: Lecture 02. Exam I. Forces: Equilibrium Examples. Today’s lecture will cover Textbook Sections 2.1-2.7. No LAB preflights this semester Discussion Quiz Free-Body diagrams and F=ma. e-mail. Did you get e-mail from me over the weekend? A) YesB) NoC) Maybe. 03. Overview. - PowerPoint PPT Presentation
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There are two forces in the diagram above that's the Force of Tension in a upward position and the Force of Gravity in a downward position. The net force of the diagram is equal to 0. So the Force of Tension minus the Force of gravity is equal to 0. (Ft- Fg = 0). (Ft=Fg). The Force of Gravity equals 550N so the Force of Tension is equal to 550. Since the Force of Tension in the String is the same throughout the Force of Tension near the scale will still be 550N.
Physics 101: Lecture 27, Pg 12
Springs ACTSprings ACT•Scale 1 reads 550 Newtons. What is the reading on scale 2?
A) 225 N B) 550 N C) 1100 N
32
In both cases the NET FORCE on the spring is zero, and the force to the right is 550N. Therefore the force to the left is also 550 N.
1 2
Physics 101: Lecture 27, Pg 13
Forces in 2 Dimensions: RampForces in 2 Dimensions: Ramp Calculate tension in the rope necessary to
keep the 5 kg block from sliding down a frictionless incline of 20 degrees.
1) Draw FBD
2) Label Axis
34
y
x
T
N
WNote, weight is not in x or y direction! Need to decompose it!
Physics 101: Lecture 27, Pg 14
Forces in 2 Dimensions: RampForces in 2 Dimensions: Ramp Calculate force necessary to keep the 5 kg
block from sliding down a frictionless incline of 20 degrees.
36
y
x
W
W sin
W cos
T
N
W
Physics 101: Lecture 27, Pg 15
Forces in 2 Dimensions: RampForces in 2 Dimensions: Ramp Calculate force necessary to keep the 5 kg
block from sliding down a frictionless incline of 20 degrees.
39
y
x
x- direction
W sin – T = 0
T = W sinm g sinNewtons
T
N
W
Physics 101: Lecture 27, Pg 16
Normal Force ACTNormal Force ACT
What is the normal force of ramp on block?
A) FN > mg B) FN = mg C) FN < mg
42
T
N
W
In “y” directionF = maN – W cos = 0N = W cos
y
x
N = m g cos
W
W sin
W cos
Physics 101: Lecture 27, Pg 17
Force at Angle ExampleForce at Angle Example A person is pushing a 15 kg block across a floor with k= 0.4 at a
constant speed. If she is pushing down at an angle of 25 degrees, what is the magnitude of her force on the block?