You are watching: Blood is accelerated from rest to 30.0 cm/s

This is university Physics Answers with Shaun Dychko. We begin by drawing a photo to highlight a item of blood that"s gift pumped by the heart and also initially, we"ll take it time, t naught, to be 0; the initial speed is 0 and also the initial place we"ll take to be 0 and also it has some acceleration which we don"t yes, really know and also then at some time later, we are told that the last speed will certainly be 30 centimeters per second at a place of 1.80 centimeters and we don"t know exactly how long the takes. So part (b) says write down the points we know so we compose down every the stuff the we know here and also I always start questions off this way anyhow and also you should also by writing down all the points that you know and a picture also helps so that"s a great problem solving strategy. Component (c) says just how long does that take for the heart to pump the blood 1.80 centimeters from remainder to a final speed the 30 centimeters per second? therefore that method the unknown is t; just how long way well, exactly how much time and so we need to choose a formula that has actually the points that we understand plus the letter t in it— the point that we want to find— and also equation 50 fits the description. Although us don"t strictly understand what the typical velocity is yet we have another formula, equation 51, to figure that out. So we space gonna solve this formula for t here so equation 50 rearranged by subtracting x naught native both sides and also then switching the sides approximately gives girlfriend this line here so v bar t amounts to final place minus early stage position and then we settle this for t by splitting both political parties by average velocity and also we have t is the last position minus the initial position split by the typical velocity. Currently this average velocity, we need to replace it with this formula and also we perform that here and also I always show substitution"s in red here. Therefore we have v naught to add v end 2 in location of v bar and then we plug in the numbers. So that"s 1.80 centimeters minus 0 centimeters— that"s the final position minus the early position— divided by the initial rate plus the final speed the 30 centimeters per 2nd divided by 2; this gives a time the 0.120 seconds. Now pay fist to her units, these are unusual units most of the moment you desire to change units right into meters, kilograms or seconds— that"s mks units— however in this case, it"s it s okay to leaving them together centimeters because we have centimeters top top the top and centimeters top top the bottom and also so they will cancel and also that will job-related out nicely to devices of seconds for ours time. And this answer does it seems ~ reasonable compared to the duration of a love pulse; if you placed your finger on your wrist and also feel your pulse, you have the right to imagine that it could last for about 0.120 seconds.

In this video, the equation $\dfracv below 0 +v 2$ is used, but the acceleration to be never discussed to be constant. Can we assume the the acceleration is constant unless otherwise stated?

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