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November 4, 2021
john hopes to finish a 10,000-m run in less than 30.0 min.after 27.0min, there are still 1100m to go. how many secods mist be consume at an acceleration of 0.20m/s^2 in order t achieve the desired time
hopes to finish a 10,000-m run in less than 30.0 min.after 27.0min, there are still 1100m to go. how many secods mist be consume at an acceleration of 0.20m/s^2 in order t achieve the desired time
University of Washington
Simon Fraser University
I) How much tension must a rope withstand if it is used to accelerate a 1210-kg car horizontally along a frictionless surface at 1.20 m/s$^2$ ?
(I) A 7150-kg railroad car travels alone on a level frictionless track with a constant speed of 15.0 m/s. A 3350-kg load, initially at rest, is dropped onto the car. What will be the car's new speed?
(II) Superman must stop a 120-km/h train in 150 m to keep it from hitting a stalled car on the tracks. If the train's mass is $3.6 \times 10^5$ kg how much force must he exert? Compare to the weight of the train (give as %). How much force does the train exert on Superman?
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Welcome to the next unit in physics 101 dynamics where we will be discussing How can we combine together our ideas of Kinnah, Matics and forces? So the reason we want to combine these is so we can analyze systems with them and make predictions about how the system is going to move. So, for example, we go back to our Kinnah Matics equations. Where we have position is a function of time is equal to initial position, plus initial velocity times, time plus one half acceleration times, time squared or we have other equations. Additionally, like V squared equals V, not squared, plus to a dealt X. Remember here that everything is labeled with X. But now that we can work in two dimensions, we could also look at these all in the why those would have to be a unique set of equations. Similarly, when we talk about forces and equations, there's really one equation. It is net force equals mass times acceleration. This is Newton's second law, and the Net force is the sum of all the forces on an object. So we're going to look at all the forces in the X direction an object all the forces in the Y direction on an object, determine its acceleration and in the X's acceleration in the UAE, and then take those results and plug them into Kinnah Matics equations. If we can. Now we're going to be looking at a lot of different forces simultaneously. There will be normal forces, intention forces, friction forces dragged. There will be standard pushes and polls. They will all be there, and we need to make sure that we're keeping track of all of them. So to do this, we're going to set up kind of a standard set of steps that we can take in order to solve these questions. First, we're going to start out by drawing free body diagrams for all the important bodies in the system. That is, if we have more than just one object being pushed. We need to consider what does the free body diagram of the other object look like? And as we write those out or draw those out, rather, we're going to have to take into account Newton's laws. So remember, we have to have Newton's first law and Newton's third law, especially where the third guys telling us we need to keep on eye on those action reaction force pairs. If we screw that up, it's going to be really hard for us to continue with the problem. Secondly, we're going to start writing out what are known as the Equations of Motion. These are the Newton's second law equations, with all the forces in the X direction adding up to mass times acceleration in the X and all the forces in the Y direction adding up to equal mass times acceleration in the UAE and, if necessary, all the forces in the Z direction adding up to equal mass times acceleration in the Z. Those will be our equations of motion. These air the equations that air really governing the motion of the object. Now we can use that then to make predictions about where the object will be at particular times, or how fast it will be moving at a particular position. And this is all fine and great, except for one thing. If our forces from part two are changing as a function of time, that means our acceleration is changing as a function of time, which means we can't use any of our nice equations from Kinnah Matics. Instead, we'll have to resort back to our our calculus equations that is say is equal to D. V, D. T and V is equal to DX DT or alternatively, the Integral Equations X is equal to the integral of E d T. And velocity is equal to the integral of a d. T. These air what we want to use whenever we have to deal with a force that is changing as a function of time, which will run into a few of those. So as long as we remember these steps, though, and keep on eye on how we do each of them, we should be able to get through each of these problems without too much difficulty.
Equilibrium and Elasticity