Unit Test 3 – Dynamics S1 2021 Instructor: Results: Gulbagh S Gulati Name: / 50 (max) (total - 65) Grade: Date: Read each Question carefully and answer all questions. No negative marking for wrong answers. Note: If there are numerical answers in any question write them upto two decimal places unless otherwise mentioned. If an answer does not have an accompanying FBD, the answer would be marked wrong, if you need any clarification / exception regarding this guideline please consult me. Make sure you show all relevant steps, if the steps are not shown the answer is deemed wrong. Q 1. While warming up for his track practice, John, with a mass of 80 kg, applied a horizontal force of 140N to speed up. Calculate his acceleration. (3) Q 2. An object is observed to have an acceleration of 2 m/s2 when a net force of 4 N is applied. The mass of the object is: (3) a. 0.5 kilogram. c. 2.0 kilograms. b. 1.0 kilogram. d. 8.0 kilograms. Page 1 Q 3. A plane reaches a takeoff speed of 95 m/s in 20s, while a fighter jet reaches 60 m/s in 3s. If both aircrafts have a mass of 6.2 X 104 kg. find the net force applied to each. (3) Q 4. Find the net force on an object that is experiencing the following forces: a. 20N [N], 40 [S] (3) b. 100N [N], 40N [W] (3) Page 2 Q 5. Three astronauts, propelled by jet backpacks, push and guide a 120 kg asteroid toward a processing dock, exerting the forces shown in figure, with F1 = 32 N, F2 = 55 N, F3 = 41 N; and θ1 is 30⁰, and θ3 is 60⁰. What is the asteroid’s acceleration? (4) Q 6. A 75kg man stand on an elevator which is accelerating upwards. The weighing scale shows a reading of 900N, what is the acceleration of the elevator? (5) Page 3 Q 7. Study the free-body diagram below and choose the statement that best describes the dynamics of the situation. (3) a. There is no net horizontal force. b. The net force acting is 30 N. c. The net horizontal force is 10 N. d. The net force acting is 6 N. e. The net force acting is 26 N. Q 8. Q 9. (3) A 10 kg block is pushed horizontally against a vertical wall, with coefficient of static friction of 0.25 between the block and the wall. With what force must the block be pushed against the wall in order to keep the block from falling? (3) Page 4 Q 10. In the figure shown, (a) calculate the acceleration of both the box A and B, if the surface is frictionless. (b) Assuming the coefficient of the friction is 0.25, calculate the acceleration of the system. (c) Calculate the coefficient of friction if the given system stays stationary (doesn’t move)? (9) Q 11. The coefficient of static friction is related to the coefficient of kinetic friction in what way? (3) a. The coefficient of static friction is always less than the coefficient of kinetic friction b. They are equal c. The coefficient of static friction is always greater than the coefficient of kinetic friction d. Not enough information Page 5 Q 12. Three toy ducks, attached to each other by a string, are being pulled by a very happy guy who just got them as a graduation present. The front duck is 5.0 kg the middle duck is 3.0 kg and the back duck is 2.0 kg. If the happy guy pulls them with a force of 15 N and there is no friction, calculate (a) the acceleration of all the ducks. (b) the tension in the string connecting duck 1 and duck 2, and duck 2 and duck 3. (7) 3 Q 13. 2 1 What is the weight on earth of a 50 kg person? (3) a. 490 N b. 9.8 N c. 50 N d. Not enough information Page 6 Q 14. Bonus 10 marks Although we don’t need the mass of the carton, but if you need it, assume it to be 1kg Page 7