/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 66 You are standing at rest at a bu... [FREE SOLUTION] | 91Ó°ÊÓ

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You are standing at rest at a bus stop. A bus moving at a constant speed of \(5.00 \mathrm{~m} / \mathrm{s}\) passes you. When the rear of the bus is \(12.0 \mathrm{~m}\) past you, you realize that it is your bus, so you start to run toward it with a constant acceleration of \(0.960 \mathrm{~m} / \mathrm{s}^{2}\). How far would you have to run before you catch up with the rear of the bus, and how fast must you be running then? Would an average college student be physically able to accomplish this?

Short Answer

Expert verified
Firstly, the student has to run a distance of approximately 25 meters to be able to catch the bus. The speed required at the moment of catching up with the bus is approximately 10 m/s. Speaking realistically, an average college student may find it difficult to reach such a speed as it is considerably fast. The students’ physical capabilities would highly come into play here, but it is generally beyond the average running speed of a human, which is around 5.6 m/s (20 km/h).

Step by step solution

01

Determine How Long the Student Takes to Catch the Bus

As we already know, the bus is moving at a constant velocity and the student is accelerating from a stationary position. So, first we have to set up two equations to determine how long it would take for the student to catch the bus: From the bus perspective, \(x_{bus} = v_b* t\) and from the student perspective, \(x_{student} = 0.5*a_s*t^2+x_o\). By setting these two equations equal to each other, we can solve for \(t\), the time it takes for the student to catch the bus. To find \(t\), we shall utilize quadratic formula \(t = \frac{-B \pm \sqrt{B^2 - 4AC}}{2A}\) where \(A = 0.5*a_s\), \(B = -v_b\), and \(C = x_o\). Once we plug in the given values, we can find the value of \(t\).
02

Determine the Student's Final Speed

The final speed (\(v_f\)) of the student when they catch the bus can be found using the equation of motion where \(v_f = a_s*t + v_i\). Given that \(v_i = 0\) m/s (as the student starts from a stationary point), the equation simplifies to \(v_f = a_s*t\). Use the value of \(t\) from step 1 and given value of \(a_s\) to find the final speed.
03

Analyzing Physical Feasibility

The last part of the problem asks for a subjective assessment of whether or not an average college student would be able to reach this speed and maintain it. There's no strict mathematical answer to this, as it would depend on a variety of factors such as the student's physical condition, but we can make an assessment by comparing the speed the student must achieve to common speeds experienced by people.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Constant Acceleration
Understanding how objects move is fundamental in physics, and constant acceleration plays a crucial role in kinematics, which is the branch of physics that deals with the motion of objects. When we talk about constant acceleration, we refer to the rate of change of velocity being steady over time. This implies that velocity is increasing or decreasing uniformly.
In our everyday experience, we often encounter constant acceleration without even realizing it. Think of an elevator starting to move, or a car speeding up - both start from rest and increase their speed in a manner that, ideally, is consistent over time. If you're standing at a bus stop and start running with constant acceleration, like in the exercise mentioned, your velocity will increase by the same amount each second. This is a classic example of constant acceleration, where the acceleration due to your effort remains uniform as you try to catch the bus.
Quadratic Formula in Physics
One might wonder what algebra has to do with catching buses, but in physics, solving kinematic problems often involves a bit of math magic, and the quadratic formula is part of that spells arsenal. This almighty tool is used when dealing with equations that include terms squared (like the positions as a function of time when acceleration is constant).
Let's say you're facing an equation like \( ax^2 + bx + c = 0 \) where \( a, b, \) and \( c \) are coefficients linked to physical quantities such as acceleration, initial velocity, and distance. The quadratic formula \( x = \frac{-b \[\pm\sqrt{b^2 - 4ac}\]}{2a} \) comes to the rescue, allowing you to find the time \( t \) at which certain events occur, like intercepting a bus. In the context of the problem we are discussing, it finds the exact moment when you, with your steady acceleration, catch up to the bus, despite it having a head start.
Equations of Motion
The equations of motion are the ABCs of kinematics. Using a set of formulas, they describe the motion of an object under the influence of constant acceleration. When solving kinematic problems, these equations can tell us information about an object's position, velocity, acceleration, and the time of travel — making them particularly handy for our bus chase scenario.
These equations include formulas such as \( v_f = v_i + at \) which calculates the final velocity \( v_f \) given the initial velocity \( v_i \) and the acceleration \( a \) over time \( t \); and \( s = ut + \frac{1}{2}at^2 \) which gives us the distance travelled (\( s \) or \( x \) in our problem). As you can see, they provide a powerful toolkit to predict the outcomes of various scenarios. If you are accelerating to catch up to the bus, these equations will determine how fast you'll need to run and how far until you're able to hop on for a ride.

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Most popular questions from this chapter

Sam heaves a 16 lb shot straight up, giving it a constant upward acceleration from rest of \(35.0 \mathrm{~m} / \mathrm{s}^{2}\) for \(64.0 \mathrm{~cm}\). He releases it \(2.20 \mathrm{~m}\) above the ground. Ignore air resistance. (a) What is the speed of the shot when Sam releases it? (b) How high above the ground does it go? (c) How much time does he have to get out of its way before it returns to the height of the top of his head, \(1.83 \mathrm{~m}\) above the ground?

The acceleration of a bus is given by \(a_{x}(t)=\alpha t,\) where \(\alpha=1.2 \mathrm{~m} / \mathrm{s}^{3} .\) (a) If the bus's velocity at time \(t=1.0 \mathrm{~s}\) is \(5.0 \mathrm{~m} / \mathrm{s}\) what is its velocity at time \(t=2.0 \mathrm{~s} ?\) (b) If the bus's position at time \(t=1.0 \mathrm{~s}\) is \(6.0 \mathrm{~m},\) what is its position at time \(t=2.0 \mathrm{~s} ?(\mathrm{c})\) Sketch \(a_{y}-t\) \(v_{y}-t,\) and \(x-t\) graphs for the motion.

An object is moving along the \(x\) -axis. At \(t=0\) it is at \(x=0 .\) Its \(x\) -component of velocity \(v_{x}\) as a function of time is given by \(v_{x}(t)=\alpha t-\beta t^{3},\) where \(\alpha=8.0 \mathrm{~m} / \mathrm{s}^{2}\) and \(\beta=4.0 \mathrm{~m} / \mathrm{s}^{4}\) (a) At what nonzero time \(t\) is the object again at \(x=0 ?\) (b) At the time calculated in part (a), what are the velocity and acceleration of the object (magnitude and direction)?

A small block has constant acceleration as it slides down a frictionless incline. The block is released from rest at the top of the incline, and its speed after it has traveled \(6.80 \mathrm{~m}\) to the bottom of the incline is \(3.80 \mathrm{~m} / \mathrm{s}\). What is the speed of the block when it is \(3.40 \mathrm{~m}\) from the top of the incline?

It has been suggested, and not facetiously, that life might have originated on Mars and been carried to the earth when a meteor hit Mars and blasted pieces of rock (perhaps containing primitive life) free of the Martian surface. Astronomers know that many Martian rocks have come to the earth this way. (For instance, search the Internet for "ALH 84001 ." ) One objection to this idea is that microbes would have had to undergo an enormous lethal acceleration during the impact. Let us investigate how large such an acceleration might be. To escape Mars, rock fragments would have to reach its escape velocity of \(5.0 \mathrm{~km} / \mathrm{s},\) and that would most likely happen over a distance of about \(4.0 \mathrm{~m}\) during the meteor impact. (a) What would be the acceleration (in \(\mathrm{m} / \mathrm{s}^{2}\) and \(g^{\prime}\) s) of such a rock fragment, if the acceleration is constant? (b) How long would this acceleration last? (c) In tests, scientists have found that over \(40 \%\) of Bacillus subtilis bacteria survived after an acceleration of \(450.000 \mathrm{~g} .\) In light of your answer to part (a), can we rule out the hypothesis that life might have been blasted from Mars to the earth?

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