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A sprinter explodes out of the starting block with an acceleration of $+2.3 \mathrm{m} / \mathrm{s}^{2}$ , which she sustains for 1.2 $\mathrm{s}$ . Then, her acceleration drops to zero for the rest of the race. What is her velocity $(\mathrm{a})$ at $t=1.2 \mathrm{s}$ and (b) at the end of the race?

(a) $v=2.76 \mathrm{m} \cdot \mathrm{s}^{-1}$(b) $v=2.76 \mathrm{m} \cdot \mathrm{s}^{-1}$

Physics 101 Mechanics

Chapter 2

Kinematics in One Dimension

Motion Along a Straight Line

Ibrahim M.

July 31, 2021

A jetliner, traveling northward, is landing with a speed of 69 m/s. Once the jet touches down, it has 750 m of runway in which to reduce its speed to 6.1 m/s. Compute the average acceleration (magnitude and direction) of the plane during landing.

Simon Fraser University

Hope College

University of Winnipeg

McMaster University

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in this problem. We have a sprinter who starts a race very strong and then finishes the race at a constant velocity. So our motions kind of divided into two parts here. So let's talk about the first part of the race first, which is the part where she is actively accelerating the whole way. Now, in order to solve any can a Matic problem, we need to find three of our five variables and then choose the equation that fits the information we're given. So the two numbers that just kind of given to us is that in the 1st 1.2 seconds of the race, she is accelerating at a positive 2.3 meters per second squared. Now, listen, before we are required to have three of these to solve, using any of the equations to the right in this case were given one of the somewhat tricky numbers that you're expected. Thio understand from the basis of the question. So it tells us that this sprinter is starting the race off with this acceleration and at the very start of the race, this sprinters, except our velocity would be zero because of the start of any race. Sprinters are always at zero. So this idea of someone starting from rest is a common mechanic of these types of problems. And it's just a way of telling us one of our variables without just giving us the number. Okay, Now, the first part question A is asking us to find the final velocity that this printer reaches during this period of acceleration. Now, to determine which equation we want to use, you look at the three numbers, you know, and the one number you want to know. And for us, that's the our final velocity and whatever equation you don't know and don't need to know, that's how you determine which can a Matic equation we're going to be using. So when I look at my list of four can a Matic equations? I'm looking for the one that does not have this accident. So those bottom three all have axe, which means that top number is where the top equation is what we're using. So to start this problem off, V equals V not plus 80 when I plug in my numbers, um, I have a final velocity is what I'm looking for. My initial was zero plus. The acceleration of 2.3 multiplied by the time of 1.2 seconds, and that gives us her final velocity of 2.76 meters per second. Okay, now, Part B says, for the rest of the race she loses that acceleration and runs at a constant velocity. And B wants to know how fast she ends the race. And this one is kind of a trick, because if she has no acceleration, her velocity is not changing any more. So that 2.76 she ended the first part at that is just the same velocity she will end the race at because no acceleration means that number is a constant.

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