Dynamics exam with key

Dynamics Provincial Exam Review Questions Key 1. A 45kg woman is standing in an elevator that is accelerating downwards at 2.0m/s². What force (normal force) does the elevator floor exert on the woman's feet during this acceleration? Fnet = Fg - T T = Fg - Fnet = 45.9 - 45*2 = 3.5 x 10² N 2. A 15kg block is pushed up a 35° incline. A friction force of 110N exists between the block and the incline. What minimum force F would be necessary to move the block up the incline at a constant speed?   Fnet = 0 = F - Ffriction - Fg sin35° F = Ffriction + Fg sin35° = 110N + 15*9.8*sin35° = 1.9 x 10² N 3. An object is sliding down an inclined plane at a constant speed. Which of the following represents the free-body diagram for the object? A. B. C. D. (This option is marked as correct)   4. A book is at rest on a desk. Which of the following statements concerning the book is correct? A. The desk exerts no force on the book. B. The book exerts no force on the desk. C. There are no forces acting on the book. D. The forces acting on the book are balanced. (✓)   5. An 810kg dragster is being decelerated by a parachute at 2.5 m/s² as shown in the diagram. T = ma = (810)(2.5) = 2.0 x 10³ N What is the tension in the cord at this moment? 6. The system of blocks on a frictionless surface in the diagram below is accelerating at 2.0 m/s².   Tpull = (Mtotal)(a) = (8kg)(2 m/s²) = 16 N Fnet = Tpull - Tx ma = 16 - Tx 4(2) = 16 - Tx Tx = 8.0 N What is the tension in the cord at X? 7. A curling rock is travelling to the right across the ice as shown in the diagram. Which of the following best represents the forces acting on the curling rock?   A. B. C. D. (✓) 8. A constant net force acting on an object results in the object having a constant A. velocity. B. momentum. C. acceleration. ✓   D. displacement. 9. An object is fired up a frictionless ramp as shown in the diagram. t = ? v₀ = 35 m/s a = -g(sin65°) If the initial velocity is 35 m/s, how long does the object take to return to the starting point? t = (vf - v₀) / a = (-35 - 35) / (-9.8 sin65°) = 7.9 s 10. Fup = Fsin25° F = Fup / sin25° = 5500 * 9.8 / sin25° = 5.9 x 10⁴ N What is the force F provided by the rotor? 11. A 15kg block has a constant acceleration of 2.2 m/s² down a 30° incline. Fnet = ma = Fgₓ - Ff Ff = Fgₓ - ma = 15 * 9.8 sin30° - 15 * 2.2 = 41 N What is the magnitude of the friction force on the block? 12. A 15kg cart is attached to a hanging 25kg mass. Friction is negligible. Fnet = mtotal * a (15+25)a = 25g a = 6.1 m/s² What is the acceleration of the 15kg cart? 13. A 15kg block on a horizontal surface has a 100N force acting on it as shown. Fn = Fg - 100N = 15 * 9.8 - 100 = 47 N What is the normal force? 14. An 18kg cart is connected to a 12kg hanging block as shown (ignore friction). (a) Draw and label a free body diagram for the 18kg cart. (b) What is the magnitude of the acceleration of the cart? Fnet = Fg + Fgx Mtotal * a = Fg + Fg a = (12*9.8 + 18*9.8*sin35°) / (18+12) = 7.3 m/s² 15. Two masses are connected by a light string over a frictionless massless pulley. There is a coefficient of friction of 0.27 between mass m₁ and the horizontal surface.   a) Draw and label a free body diagram showing the forces acting on mass m₁. free body diagram with forces: F_T (tension), F_g (gravity), F_N (normal force), and F_f (friction) b) What is the acceleration of mass m₁? m₁a = m₁g - μm₁g a = g(1 - μ) = 9.8(1 - 0.27) = 7.1 m/s² 16. A block is on a frictionless incline. Which of the following is a correct free body diagram for the block? four free body diagrams, with one marked as correct Correct answer: The diagram shows only two forces acting on the block: the force of gravity (mg) acting vertically downward and the normal force (N) acting perpendicular to the incline.