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**Unformatted text preview: **PHYS 2101 Spring 2011 I. Work-Energy Theorem II. Conservative Forces III. Potential Energy
IV. Conservation of Energy PHYS 2101 CT1: Spring 2011 Does the force shown do positive, negative, or zero
work as the block slide up the ramp?
1. Positive 2. Negative ∆r F 3. Zero PHYS 2101 CT2: Spring 2011 Does the force shown do positive, negative, or zero
work as the ball falls straight down?
1. Positive 2. Negative F
∆r 3. Zero PHYS 2101 EX0: Spring 2011 If the rope being pulled by Moe has a tension of 140
N and lies along a line at an angle of 32° with the
horizontal and Larry pushes with a 100 N force, how
much work does friction do on the 50-kg box as it
moves 7.5 m across the room if it started at rest and
is traveling at 4.0 m/s at the end of 7.5 m? PHYS 2101 Spring 2011 Work
Net Energy
Change ∆K Speed v. Positive Adds Kf > Ki Speeds
up Same
direction Negative Subtracts Ki > Kf Slows
down Opposite
directions No work No
change Kf = Ki Same
speed Perpendicular PHYS 2101 Spring 2011 velocity (m/s)
position (m) 2 10 30 time (s) time (s) 60 80 PHYS 2101 Spring 2011 Force (N)
position (m) 2 10 30 time (s) position (m) 60 80 Spring 2011 Velocity (m) Net Force (N) PHYS 2101
10 -5
10 20 Time (s) position (m) 30 40 CT3: The change in the kinetic energy of an object
whose force v. time graph is shown above is...
1. 0 J 4. 75 J 2. 25 J 5. 100 J 3. 50 J 6. 175 J 50 PHYS 2101 CT4: Spring 2011 You
You need to load a heavy box from the ground onto
the back of a pickup truck. You can (A) lift it straight
up, (B) slide it up a steep, short ramp, or (C) slide it
up a long frictionless ramp. What is the correct
order for the work done by gravityeach case?
you in in each case?
1. WA>WB>WC 2. WA<WB<WC 3. WA>WB=WC 4. WA=WB=WC A
B C PHYS 2101 EX1: Spring 2011 A 15.0 kg box initially sits at the bottom of a
frictionless ramp. It is pulled by a cable to the top of
the ramp, which is 2.5 m higher than the bottom of
the ramp, and brought to a stop. How much work
does each force acting on the box do during the lift? PHYS 2101 CT5: Spring 2011 Where does the spring do positive work? The
equilibrium point is at x=0. (Answer all that apply)
As the block moves from:
1. From xa to x=0
2. From x=0 to xb
3. From xa to xb 4. From x=0 to xa 5. From xb to x=0 6. From xb to xa xa x=0 xb +x PHYS 2101 CT6: Spring 2011 You are standing on a platform that stands 5 meters
above the ground. You throw a 0.4-kg ball off the
platform with an initial speed of 25 m/s. In which
direction should you throw the ball so that it has the
largest speed when it hits the ground?
1. 4. 2. 5. 3. 6. PHYS 2101 EX2: Spring 2011 You throw the 0.4-kg ball horizontally off the 5-m
platform at 25 m/s. What speed is the ball traveling
when it hits the ground? PHYS 2101 EX3: Spring 2011 A block of mass m = 0.50 kg slides across a
horizontal frictionless table with a speed of v = 2.0
m/s. It runs into a spring with a spring constant k =
750 N/m. What is the maximum distance the spring
is compressed? PHYS 2101 EX4: Spring 2011 A block of mass m = 0.50 kg drops onto a platform
supported by a spring with a spring constant k = 750
N/m. The mass is traveling at 2.0 m/s when it hits
the platform. What is the maximum distance the
spring is compressed? PHYS 2101 EX5: Spring 2011 A runaway truck with failed brakes is moving at 35
m/s just before the driver steers the truck up an
emergency ramp with an inclination of θ = 15°. The
truck’s mass is 1.2 x 104 kg. What minimum length
must the ramp have to stop the truck if µ k = 0.85? PHYS 2101 CT7: Spring 2011 If
If you increase each of the following quantities, will
the distance the ramp needs to be to stop the
truck...?
1. Increase 2. Decrease 3. Remain the Same
A. Initial speed of the truck
B. Coefficient of kinetic friction
C. Mass of the truck
D. Angle of inclination PHYS 2101 EX6: Spring 2011 Two blocks are placed on at Atwood machine, one
with a mass of 4 kg and the other with a mass of 5
kg. If both blocks are initially placed at the same
height, what is the speed of the heavier block after it
has fallen 1.5 meters? ...

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