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Lyzinski An extensive review for the upcoming test Accel Physics Newton’s Laws with Friction Review Worksheet 1. Answer each of the questions below. a) What is the net force required to give an automobile of mass 1600 kg an acceleration of 4.5 m/s 2? b) What is the acceleration of a wagon of mass 20 kg if a horizontal force of 64 N is applied to it (ignore friction)? c) What is the mass of a block of iron if a net force of 240 N causes it to accelerate across a smooth horizontal surface at 2.5 m/s2? 2. Why must an object at rest have either no force or a minimum of two forces acting on it? 3. A 50 kg wood block is being dragged at an angle of 20 o above horizontal across a wood floor, where the coefficient of friction is 0.5. The dragging force is 75N. Find the acceleration of the block. 4. A 20 kg object is at rest. A force of 200 N is required to set the block in motion. Once the object is in motion, it will maintain a constant velocity as long as a 150 N acts upon it. Find the coefficients of static and kinetic friction between the object and the floor. 5. A 3.0 kg toy is pulled by a force of 24 N. If the toy starts from rest, how far will it travel in the first 5.0 s? 6. A 40 kg sprinter starts from rest and 2.0 s later is running at a speed of 8.0 m/s. What is the average net horizontal force acting on her? What exerts this force? 7. A 70 kg hockey player coasts along the ice on steel skates. If the coefficient of kinetic friction is 0.010, what is the force of friction? How long will it take him to coast to a stop, if he is traveling at 1.0 m/s? 8. A boy pulls a 50 kg crate across a level floor with a force of 200 N. If the force acts at an angle of 30° up from the horizontal, and the coefficient of kinetic friction is 0.30, determine a. the normal force exerted on the crate by the floor b. the horizontal frictional force exerted on the crate by the floor c. the acceleration of the crate 9. An 8.0 g bullet traveling at 400 m/s passes through a heavy block of wood in 4.0 x 10 –4 s, emerging with a velocity of 100 m/s. Ignore any motion of the wood. a) with what average force did the wood oppose the motion of the bullet? b) how thick is the block of wood? 10. A 0.22 caliber rifle shoots a bullet of mass 1.8 g with a muzzle velocity (exit velocity) of 500 m/s. If the barrel is 25 cm long, what is the average force exerted on the bullet while it is in the barrel? 11. SKIP 12. SKIP 13. SKIP 14. A child’s wagon experiences a frictional force of 73 N whenever it is in motion, regardless of the load it is carrying. An applied horizontal force of 128 N causes the wagon to accelerate at 5.0 m/s 2. The same applied force, with a child on the wagon, causes it to accelerate at 1.0 m/s2. What is the mass of the child? 15. A 10 kg box is pushed with a 50 N horizontal force. The coefficient of friction between the box and the ground is 0.4. Determine the acceleration of the box. 16. A 45 N force is applied to a 10 kg toy causing it to accelerate at 0.58 m/s 2. Determine the coefficient of friction. 17. A 15 kg box falls off the back of a truck traveling at 20 m/s. It comes to rest in 12 meters. Determine the coefficient of friction between the box and the road. 18. A gardener pushes down along the handle of a lawn mower of 20 kg mass with a force of 150 N. The handle makes an angle of 60° with the ground. Calculate the instantaneous acceleration of the mower if the frictional force between its wheels and the ground at that instant is 25 N. 19. A man drags a package across the floor by pulling it with a rope. He pulls with a force of a 40 N, but there is an angle between the rope and the ground. The mass of the package is 10 kg. If the acceleration of the package is 3.5 m/s 2, and friction can be neglected, at what angle to the horizontal does the man pull? 20. A boy with a mass of 30 kg pulls a cart with a mass of 100 kg towards himself by a rope. With what force does he have to pull on the rope to accelerate the cart at 2.0 m/s2? With what force must his feet push on the ground to keep him from moving towards the cart? If there is no friction between his feet and the ground, what is his acceleration? 21. A 12 kg sled is being pulled by a 100 N force at an angle of 50 o above the ground. The coefficient of friction between the sled and the ground is 0.4. a) Draw the free-body diagram of the sled showing all the forces acting upon it. b) Determine the acceleration of the sled. 22. A 1200 kg car has new tires, which have a coefficient of friction of 0.45. a) If the car is traveling at 20 m/s, determine the distance required to for the brakes (friction) to stop the car. b) How far would the car take to stop if it had an initial speed of 60 m/s? 23. SKIP 24. An F-14 Tomcat reaches speeds of 74 m/s from rest in a distance of 305 meters from the deck of an aircraft carrier. The Tomcat has a mass of 27,000 kg at takeoff. Determine the necessary force for takeoff. (FYI: this force is supplied by the twin jet engines and the tow-line power by steam) 25. The same airplane from problem #34 comes to rest while landing in 2 seconds. It is landing at 67 m/s and then comes to rest on the dock of the aircraft carrier. What is the force of the Toe-hook acting on the plane as it brings it to rest? 26. A 38 kg skater traveling at 20 m/s falls on his rear-end and slides to rest in 10 seconds. a) Determine the force of friction between the skater and the ice. b) Draw a free-body diagram of the skater showing all the forces while sliding. 27. A 9-month-old boy is pushing down on his Fisher-Price Popcorn Popping walker toy. The toy has a mass of 4 kg and is moving with a constant velocity of 2.3 m/s. The boy is pushing down with a force at an angle of 45 o with respect to the ground. There is a frictional force of 30 N acting on the toy. Determine the force of the boy acting on the handle. 28) A train of three cars ( each of mass 500 kg) is being pulled across a surface whose coefficient of kinetic friction is 0.3. If the tension in the last coupling is 1600 Newtons, find… a) the acceleration of the train. b) the force that the train is pulled with. c) the tension in the other coupling. 29) Three boxes, each of mass 70 kg, are pushed into each other. The force between the first box (to which the external force is applied) and the second box is 400N. If the surface they are pushed on is frictionless, find … a) the acceleration of the blocks. b) the external force that they are pushed with. c) the force between the 2nd and 3rd boxes. ** Full solutions are available online