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University of Michigan - Ann Arbor
University of Sheffield
(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) A person has a reasonable chance of surviving an automobile crash if the deceleration is no more than 30 $g$'s. Calculate the force on a 65-kg person accelerating at this rate.What distance is traveled if brought to rest at this rate from 95 km/h?
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welcome to our last section considering work and energy or at least our introduction to work and energy. And this section will be considering power. So power is used in a lot of ways in common language that it doesn't mean physically, Just like work is used in many ways, um, in common language that it doesn't mean physically or at least physically so. Power here, though, is defined as amount of work done over a certain amount of time. And when we look at this, there's a couple of reactions you might have quickly. First of all, we have a work divided by a delta t here, and you'd be right in thinking that Well, work is equal. Thio change in kinetic energy and work itself is in jewels here. So first of all, our units are gonna be jewels per second. Okay, which we refer to as Watts. It's the S I unit called Watts, which is a capital w. You may have heard of Watts before, or Kilowatts. It shows up on a lot of appliances and other electron ICS and understanding what this means will allow us to figure out exactly how much energy those appliances are using or producing if you're talking about solar panels. On the other hand, if we look at this and we're thinking about work with respect to time, we can actually turn this into a derivative if we think of a very small amount of time, so that could be very helpful here. Also plugging things in we have f Delta X cosine theta divided by Delta T. These are magnitudes which we could then rewrite as f Delta X over Delta T. Because I Impenetrable Delta X over Delta T if it gets very small is just velocity. So power is actually equal to F dotted into velocity as well. So we now have three equations here for calculating power, uh, one with algebra, one with a dot product, one with calculus. So we're going to take a look at how to use all three of these equations in the coming videos to calculate power and what we can take from a power measurement to figure out about energy use
Equilibrium and Elasticity
Moment, Impulse, and Collisions
Rotation of Rigid Bodies