Unit 6: Friction and Spring Force Review Section 1: Know the definitions and/or concepts of the following: 1) Static friction force:

Transcription

1 Name Date Period Unit 6: Friction and Spring Force Review Section 1: Know the definitions and/or concepts of the following: 1) Static friction force: 5) Hooke s Law: 2) Kinetic friction force: 6) Spring constant: 3) Coefficient of kinetic friction: 7) Newton s third law: 4) Coefficient of static friction: 8) Equilibrium: 9) You push on a piano at rest and the piano does not move. You push on it even harder and still the piano does not move. a) Explain what is preventing the piano from moving. b) What is required for the piano to start moving? 10) A toy car is pressed into a spring that is attached to a wall. The car compresses the spring. Which direction is the spring force acting on the toy car? a) Toward the wall b) Away from the wall c) The spring force is equal to zero 11) Identify the action-reaction pair: a) A rocket in space pushes gas backward. As hard as the rocket pushes on the gas... b) A little boy pulls on a wagon. As hard as the little boy pulls on the wagon...

2 12) Write 1 st, 2 nd or 3 rd in each blank to indicate which of Newton s laws applies in this situation. a) A jerk at a sporting event is hit in the face by his not-so-good friend. His not-so-good friend s hand is broken in the process. b) A bully finds than he can throw a low mass physics nerd farther than he can a high mass physics nerd. c) A bullet strikes a concrete wall. The wall is chipped and the bullet is flattened. d) A young boy pulls his triple scoop ice-cream cone away from his baby brother and the top scoop falls straight down over where the cone originally started. e) A marksman notices that if he puts less gunpowder in the casing of a bullet, the bullet will be traveling slower when it leaves the barrel of a gun. Section 2: Work through each of the following problems. Show your work and include units on all solutions. 13) A box of mass 52 kg is pulled along flat ground. The static friction coefficient is 0.74, and the kinetic friction coefficient is c) What magnitude of force will be needed to keep the box moving at a constant velocity? d) What magnitude of force will be needed to start the box moving?

3 14) If you use a horizontal force of -720 N to slide a 95 kg wooden crate across a floor at a -4.5 m/s 2 acceleration, c) Find the magnitude of the friction force acting on the crate. d) What is the coefficient of kinetic friction between the crate and the floor? 15) A daredevil attaches a spring to his belt that has been pulled straight down from its equilibrium position. The daredevil weighs 1050 N and the spring constant of the spring is 525 N/m. The Daredevil is released and at a given point the acceleration of the daredevil is 2.7 m/s 2, upward. c) Find the spring force acting on the daredevil at the point described in the situation. d) Find how far the spring is stretched when the acceleration of the daredevil is 2.7 m/s 2, upward. Give the stretch in both meters and centimeters.

4 16) A 50 gram block is pulled with a spring with an acceleration in the direction of motion of 0.5 m/s 2 across a level surface. If the coefficient of kinetic friction between the two surfaces is 0.4 and the spring is stretched 2.5 cm from its equilibrium position: c) Find the magnitude of the spring forces acting on the block. d) Find the spring constant of the spring. 17) A 75 kg student on roller skates throws a 10 kg medicine ball with an acceleration of 2 m/s 2. a) What is the magnitude of the net force that acts on the medicine ball? b) What is the net force that acts on the student? c) What is the magnitude and direction of the acceleration of the student?

5 18) A student buys a new spring at the hardware store and wishes to find its spring constant. The spring is stretched by 15 cm and the force required to stretch the spring is recorded in Table 1. The spring is then stretch another 15 cm and the force is again recorded. This procedure is repeated several times and the data is recorded in Table 1. a) Graph the Applied force (Y-axis) vs. the amount of stretch (X-axis) on the graphs provided. Make sure you have decent scales and have labeled your axes for each graph. Draw a best fit straight line for each graph. Table 1: Spring Spring: Applied Force Vs Stretch Graph Amount of stretch in meters Force applied to spring in newtons b) The slope of the Applied Force-Stretch graph is equal to the spring constant. Find the value of the spring constant using the slope of the graph and express your answer in units of N/m. The Review Continues onto the next page.

6 19) You wish to find the coefficient of static and kinetic friction between denim jeans and a blowup slide. You take an old pair of denim jeans and cut a square from the leg. The manufacturer of the blowup slide sends you a three foot sample of the material they use to make the slide. You secure the slide material to a flat table top and set the denim sample on top. You then add a 0.5 kg mass on top of the denim sample. You apply a horizontal force to the denim sample with a spring scale and slowly increase the pull. You note the force at which the denim just starts to slide as the maximum static friction force and call out the number for your friend to record. You then allow the denim to slide at a constant speed over the slide material. You note this force as the kinetic friction force and call out the number for your friend to record. You then place another 0.5 kg mass on the denim sample and do the experiment again. You repeat the experiment three more times adding 0.5 kg to the denim sample for each trial. The data table below contains the information from this experiment. 0.5 kg 1.0 kg 1.5 kg 2.0 kg 2.5 kg Mass of Weights (kg) Normal Force (N) Maximum Static Friction Force (N) Kinetic Friction Force (N) a) Make a graph with the kinetic friction force on the y-axis and the normal force on the x-axis. Set a scale and label the axis. Use as much of the graph as possible. (Use a straight edge to draw a line of best fit through the data.) c) Make a graph with the max static Friction force on the y-axis and the normal force on the x-axis. Set a scale and label the axis. Use as much of the graph as possible. (Use a straight edge to draw a line of best fit through the data.) b) The slope of the Kinetic Friction-Normal Force graph is equal to the coefficient of kinetic friction. Find the slope of the graph and record the value below. d) The slope of the Max Static Friction-Normal Force graph is equal to the coefficient of static friction. Find the slope of the graph and record the value below.