Homework 1) A crate of mass 20 kg is being pushed by a person with a horizontal force of 63 N, moving with a constant velocity. Find the coefficient of kinetic friction. [0.32] 2) Calculate the force required to start pushing a fridge of mass 100 kg if the coefficient of static friction, H. = 0.46. [Fa > 451 N] 3) A box of mass 5.7 kg slides across a floor and comes to a complete stop. If its initial speed was 10 kim/h and is = 0.34, find: al The friction acting on the box. [19 N] by The acceleration of the box. [-3.3 m/s'] c) The distance travelled by the box before stopping. [1.2 m] d) The time it took to stop. [0.83 5] 4) What force is required to accelerate a lawnmower of mass 12 bg to 4.5 km/h from rest in 3.0 s (neglecting friction)? [5.ON] a] If there is friction present and po= 0.80, what force is required now? [99 ] 5] A book (m =1.1 kg) is being pushed across a table. A force of 30 N is pushing down on the book, while a force of 240 N is pushing to the right. Calculate the acceleration of the book if the coefficient of friction is 0.45. [201.5 m/s'] 6] Two children are pushing a 80 kg sled across the ice. One is pushing with a force of 120 N [left] while the other is pushing with a force of 22 5 N [right]. The coefficient of friction is 0.05. Calculate the resulting acceleration of the sled. [0.73 m/s' right] 7) A 45 kg cart has an acceleration of 3.5 my's [right] when a force of 250 N [right] and 25 N [left] is applied to it. Calculate the coefficient of friction. [0.15] 2) Calculate the force is required to accelerate a 1200kg car from 5 m/'s to 17 m/'s in 6.4 seconds if the coefficient of friction is 0.45. [7542 N] Also do the following from textbook pg 171 #1-3 Practice 1. Determine the coefficient of friction for each situation. [a) It takes a horizontal force of 62 N to get a 22 by box to just start moving across the floor. [ans: 0.29] (b) It only takes 58 N of horizontal force to move the same box at a constant velocity jai uin] 2. A 75 by hockey player glides across the los on his skates with steel blades. What is the magnitude of the force of friction acting on the skater? Use Table 1 to help you. al jars 74 M 3. A 1300 kg car skids across an asphalt road. Use Table 1 to calculate the magnitude of the force of friction acting on the car due to the road if the road is (a) dry laree 60OO N to 10 000 N] ibj wet june 1200 N 1 8000 M (c covered with ice [ans:64 M