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04:15

Kathleen Tatem

(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?

03:04

Kai Chen

(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?

00:39

Averell Hause

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$^2$ ?

04:39

Muhammed Shafi

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welcome to our fourth example video. Looking at excited states in this video, we're going to say that we have a flash lamp which has excited a number of electrons and not which is going to be equal to two times 10 to the seven. So we have two times 10 to 7 electrons that have been excited into ah higher state, which has a lifetime of 14 nanoseconds. And we'd like to find how long? If the flashlight goes off AT T equals zero, how long will it take to lose half of these excited states? Remember that and excited is equal to end, not times e to the negative t over tau. Which means if we want and excited to be one half and not then then we take one half times and excited is e. I apologize one half times and not is what we want and excited to be equal to is going to be equal to end not times e to the negative. T over Tau are in knots. Cancel out. We can take the natural log of both sides so we have natural log of one half is equal to negative t over town which means we're going to end up with T, is equal to Tao Times, the natural log of to notice here that we've used the natural log rules where a negative natural log of a over B is equal to the natural log of be over a typing this in then with the Tao of 14 times 10 to the negative nine seconds multiplied by the natural log of to what we come back with is 9.7 nanoseconds. So not even 10 nanoseconds later. We've already lost half of our excited states.

Nuclear Physics

Condensed Matter Physics