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Transcript

SPH3U Dynamics Unit Assignment Name: _____________ 1. A force of gravity of 20 N [down] acts on a book at rest on a rough level table. A horizontal force of 12 N is needed to just start the book moving across the table. a) Calculate the coefficient of friction. b) If a second identical book is placed on top of the original book at rest, what horizontal force would be needed to just start the books sliding? 2. A 1000 kg crate is dragged across a rough level floor. A force of 450 N is needed to drag the crate at constant speed. Calculate the coefficient of kinetic friction between the crate and the floor. 3. A car of weight 1500 N has its brakes locked. Calculate the force needed to begin to drag it on dry asphalt. How will the force needed to slide it along the asphalt compare with the force needed to start it sliding? 4. An 80 kg skier is using waxed hickory skis on wet snow. Calculate the force of friction on the skis as the skier glides along on the level. Material Copper on copper Steel on greased steel Steel on dry steel Oak on oak Rubber tire on dry asphalt Rubber tire on wet asphalt Rubber tire on dry concrete Rubber tire on wet concrete Rubber tire on ice Teflon on Teflon Waxed hickory skis on dry snow Waxed hickory skis on wet snow Coefficient of Friction Static μs Kinetic μk 1.6 1.0 0.15 0.09 0.41 0.38 0.5 0.3 1.2 0.8 0.6 0.5 1.0 0.7 0.7 0.5 0.006 0.005 0.04 0.04 0.06 0.04 0.20 0.14 5. How are mass and inertia related? 6. A curler exerts a force forward on a 19 kg curling stone and gives it an acceleration of 1.8 m/s2 [forward]. Given μk = 0.080 [back], calculate the value of the applied force. 7. A truck skidding on wet asphalt has a mass of 2000 kg. The total force of kinetic friction of the asphalt on the tires is 1000 N [back]. Calculate the deceleration of the truck. 8. A net force of 2.2 × 102 N [W] applied to an object increases its velocity from 8.0 m/s [W] to 24 m/s [W] in 5.4 s. What is the mass of the object? 9. A person applies a force of 8.0 N [S] to give a 2.5 kg sled an acceleration of 3.0 m/s 2 [S]. Calculate the force of kinetic friction. 10. A small horizontal force of 30 N is applied to box A (25 kg) which also pushes onto box B (15 kg). The boxes sit on a smooth surface, and then accelerate forward at 0.75 m/s2. What size of forces do the boxes exert on each other? 11. A force of 300 N is applied to a 50 kg box on a rough floor. The frictional force is 200 N. a) Calculate the acceleration of the box. b) If the 300 N force is removed after 4.0 s, how long will it take the box to come to rest?