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### Physics 1

 0 Look around your house for examples; what are the applications of the following topics of Physics 1: Unit conversion Example: converting miles to km and vice versa when you travel in a foreign country Equations of motion Example: Google maps and GPS devices use equations of motion to calculate estimated-time-of-arrivals (ETAs) Newton's Laws of motion Forces Momentum Angular Momentum Energy and Work Rotational Motion Show answer Think about your everyday activities. Everybody uses physics and engineering everyday ! 1 What is the SI unit for the following quantities? Force Distance Speed Time Volume Mass Show answer Force - 'N' for Newtons Distance - 'm' for meters Speed - 'm/s' for meters per second Time - 's' for seconds Volume - 'm3' for cubic meters Mass - 'kg' for kilograms 2 What is the weight of 1kg? Show answer Multiply mass by 9.8 m/s2 (which is also 9.8 N/kg) 3 Sketch position-time diagrams showing: Constant and positive velocity Positive and increasing (acceleration) velocity Negative velocity, increasing in the negative velocity (deceleration) Negative velocity, decreasing in the negative velocity (acceleration) Show answer Check suggested position-time (p-t) graph solutions at Physicsclassroom.com 4 Sketch velocity-time graph showing the following: Positive velocity and zero acceleration Positive velocity and constant positive acceleration Negative velocity and zero acceleration Negative velocity and constant positive acceleration Negative velocity and constant negative acceleration (deceleration) Positive velocity and constant negative acceleration (deceleration) Show answer Check shapes and slopes of velocity-time graph solutions at Physicsclassroom.com for suggested solutions 5 What is the significance of the area under the following graphs: Velocity-time graph Acceleration-time graph Show answer Area under a v-t graph is equivalent to change in displacement. Contact River Hawk Tutors for a detailed solution 6 Draw free-body diagram of following: Hint: for each statement, you can draw 2 free-body diagrams, for example, a man pushing a fridge; you can draw free-body diagram (1) for the man and another one (2) for the fridge A man pushing a fridge A book on a table Yourself sitting on a chair A car that is skidding to a complete stop A box that is sliding down on an inclined plane A satellite orbiting around the earth A brick that is free-falling from the top of a building A tow truck towing your car with a chain link Yourself riding down an elevator that is moving at constant speed Yourself riding down an elevator that is increasing in speed Show answer Answers to select problems are shown below 7 What is the definition of momentum? Show answer Check your textbook or refer to class notes. 8 Did you know that iRobot (located on route 3 in Bedford) makes robots called Braava and Roomba that sweep and mop your floor by themselves? Assume you have one of those robots at home. When you forget your laptop at home, your ‘smart’ cat learns (from watching some YouTube videos) how to ride the robot while the robot is cleaning the floor. Assume your cat weighs 2 kg and the robot weighs 1.8 kg. Imbed video here. If the Roomba is moving at a speed of 30cm/s without the cat, what is the total kinetic energy of the Roomba? The cat quickly jumps on top of the Roomba as the Roomba makes a turn around a couch in the living room. If the Roomba has a constant speed of 30cm/s, what is the new total kinetic energy of the Roomba carrying a cat? After it senses that the cat is getting a free joy-ride, your Roomba decides to make the cat dizzy by moving in circular motion at a speed of 30cm/s about the center of the robot as shown below. Eventually the cat falls off from dizziness. Calculate the angular speed of the Roomba if the Roomba has a radius of 0.15cm. Awww, the poor cat :-( Draw free body diagram of the Roomba as seen from the side and assuming that there is friction between the Roomba and the floor.The Roomba is moving in a straight line at constant velocity(draw just the Roomba) Draw free body diagram of the cat (draw just the cat and the forces) The Roomba uses very complicated sensors to know that it has collided with something in the house. It so happens that after dropping your ‘cat’ in part c, the Roomba collides with your dog that was sleeping on the floor. The Roomba quickly decides to go back in the opposite direction at a velocity of -30cm/s. Calculate the change in momentum of the Roomba Show answer Do not be so much concerned about getting the numerical answer, attempt questions and document your approach. Contact River Hawk Tutors for a detailed solution 9 Write the formulae for calculating total kinetic energy of a circular disc and a box. Assume both the disc and the box have the same mass, M, and translational velocity, v. Show answer Review textbook chapter on translational and rotation kinetic energy. A rolling disk has translational and rotation kinetic energy whilst a sliding box only has translational kinetic energy. 10 Additional Problems:
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