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(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?
(I) What force is needed to accelerate a sled (mass = 55 kg) at 1.4 m/s$^2$ on horizontal frictionless ice?
(II) According to a simplified model of a mammalian heart, at each pulse approximately 20 $g$ of blood is accelerated from 0.25 m/s to 0.35 m/s during a period of 0.10 s. What is the magnitude of the force exerted by the heart muscle?
(I) A 110-kg tackler moving at 2.5 ms meets head-on (and holds on to) an 82-kg halfback moving at 5.0 m/s. What will be their mutual speed immediately after the collision?
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welcome to our first example video. Considering power in this video, we're going to talk about appliances. Um, many appliances have wattage is written on the side. For example, if you go look at your TV, you'll probably find that it has a wattage somewhere on the order of a couple 100 watts to several 100 watts written on the side. Eso Let's say you have your TV and it's using 200 watts of electricity, so that's 200 jewels per second. And I want to find out if I leave my TV on for three hours. How much is that going to cost me now? Depending on where you live, electricity might cost anywhere from eight or nine cents per kilowatt hour to 20 cents per kilowatt hour. Let's go ahead with just 10 cents per kilowatt hour kilowatt hour. Here. What it means is literally what it says a kilowatt times one hour. So that's 1000 watts times one hour, which is 3600 seconds. Notice that Watson's jewels per second were multiplying by time, which means we end up with 3.6 times 10 to the six. Jules is what's in a kilowatt hour. So this is a lot of jewels, and it be annoying to write this down on all of your energy bills. Which is why, if you live in the United States, at least your power bill is reported in terms of kilowatt hours. Um, some other countries use other units, but this is by far the most common one. So, uh, let's come over here and figure out how much it costs to leave your TV on for three hours. So we have 200 watts of power. Remember, that's jewels per second, and then we have an amount of time. So let's go ahead and multiply 200 watts by the amount of time. So that's three hours now. Watson's jewels per second. So we want to convert this into seconds. To do that, we go 3600 seconds per hour, then multiplying it in. We're able to come up with a number of jewels, but what we really want is a number of kilowatt hours. So we see the conversion right here. We see that there are 3.6 times 10 to the six Jules in one kilowatt hour, and then we can multiply by all the amount of money per kilowatt hour here. So that's 0.10 divided by one kilowatt hour. So kilowatt hours canceled. Jewels would cancel seconds. We'll cancel with Watts. Remember of Watts joules per second and we're left with just dollars as the number that's left over here. So we have 200 times three times 3 36 100 divided by 3.6 times 10 to 6, all times 60.1. So it doesn't look like it's gonna be very much. You can take a look and see how maney sense it cost you to leave your TV on for a few hours.
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