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lecture5_tth_2101_S11

# lecture5_tth_2101_S11 - PHYS 2101 Spring 2011 I Work-Energy...

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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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