lecture4_tth_2101_S11

lecture4_tth_2101_S11 - PHYS 2101 Spring 2011 I. NSL with 2...

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Unformatted text preview: PHYS 2101 Spring 2011 I. NSL with 2 or more objects I. Circular Motion I. Centripetal Acceleration I. Work and Kinetic Energy PHYS 2101 Spring 2011 A block of mass m1 rests on a rough inclined plane and is attached to a hanging mass of mass m2 by a string which is draped over a frictionless, massless pulley. If the coefficient of kinetic friction between m1 and the plane is µ k, how long will it take m2 to fall a distance d to the floor? m1 = 10 kg m2 = 20 kg θ = 30 µ k = 0.5 d = 1.2 m m1 m2 d θ PHYS 2101 EX1: Spring 2011 A conical pendulum with a 0.25 kg mass attached to the end of a 0.6 m long string swings with a period of T = _____ s. What is the angle the string makes with the vertical? PHYS 2101 Spring 2011 CT1: A small child of mass 31 kg swings back and forth on a rope swing whose length is 3.8 m. At the bottom of each swing (i.e., when the rope is vertical), her speed is 4.2 m/s. When she is at the bottom of each swing, in which direction is the child accelerating? 1 - To the left 2 - To the right 3 - Up 4 - Down 5 - It depends on which way she is swinging 6 - She is not accelerating at that instant PHYS 2101 Spring 2011 CT2: A small child of mass 31 kg swings back and forth on a rope swing whose length is 3.8 m. At the bottom of each swing (i.e., when the rope is vertical), her speed is 4.2 m/s. When she is at the bottom of each swing, what can we conclude about the forces involved? (There may be more than one correct answer.) 1 - The tension is greater than her weight 2 - The tension is equal to her weight 3 - The tension is less than her weight 4 - The centripetal force is due to the tension 5 - The centripetal force is due to gravity PHYS 2101 EX2: Spring 2011 A small child of mass 31 kg swings back and forth on a rope swing whose length is 3.8 m. At the bottom of each swing (i.e., when the rope is vertical), her speed is 4.2 m/ s. What is the magnitude of the tension in the rope at the instant when she is at the bottom of each swing? PHYS 2101 CT3: Spring 2011 Which forces shown below do positive work on an no work work object negativeon an on an with the given given displacement? object with thedisplacement? 1 - F1 2 - F2 F1 F4 3 - F3 F2 4 - F4 5 - None of them ∆x F3 PHYS 2101 CT4: Spring 2011 Which forces shown below do positive work on an no work work object negativeon an on an with the given given displacement? object with thedisplacement? 1 - F1 2 - F2 F1 F4 3 - F3 F2 4 - F4 5 - None of them ∆x F3 PHYS 2101 CT5: Spring 2011 As As the Three Stooges Moving Company push and pull against a stationary box, which forces acting on the box do no work?work? positive negativework? 1. 1. Fg 2. FN 3. FL 4. FC 5. fk 6. T Curly Moe Larry PHYS 2101 CT6: Spring 2011 As As the Three Stooges Moving Company slides the box across the floor, which forces acting on the box do no work?work? positive negativework? 1. 1. Fg 2. FN 3. FL 4. FC 5. fk 6. T Curly Moe Larry PHYS 2101 EX3: 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, how much work does Moe do on the box as it moves 7.5 m across the room? PHYS 2101 EX3: 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 at a constant speed? PHYS 2101 EX3: 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 EX4: 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 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 ...
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