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In a test run, a certain car accelerates uniformly from zero to \(24.0 \mathrm{~m} / \mathrm{s}\) in \(2.95 \mathrm{~s}\). (a) What is the magnitude of the car's acceleration? (b) How long does it take the car to change its speed from \(10.0 \mathrm{~m} / \mathrm{s}\) to \(20.0 \mathrm{~m} / \mathrm{s} ?\) (c) Will doubling the time always double the change in speed? Why?

Short Answer

Expert verified
The acceleration of the car is \(\frac{24.0 m/s}{2.95 s} \) m/s². It takes \(\frac{10.0 m/s}{ a }\) seconds to change its speed from 10.0 m/s to 20.0 m/s. Doubling the time does not necessarily double the change in speed due to the nature of acceleration.

Step by step solution

01

Calculate Acceleration

The formula for acceleration is \(a = \frac{v - u}{t}\), where 'v' is the final velocity, 'u' is the initial velocity, and 't' is the time taken. Here, v = 24.0 m/s, u = 0 m/s (because the car is initially at rest), and t = 2.95 s. Substituting these values into the formula, we get \(a = \frac{24.0 m/s - 0 m/s}{2.95 s}\).
02

Calculate Time to Change Speed

To calculate the time it takes for the speed of the car to change from 10.0 m/s to 20.0 m/s, we need to rearrange the formula to solve for time. The rearranged formula is \(t = \frac{v - u}{a}\). Substituting in the acceleration we found in Step 1 and the given values, we get \(t = \frac{20.0 m/s - 10.0 m/s}{a}\).
03

Consider Effect of Doubling Time

Doubling the time does not always double the change in speed. This is because acceleration is the rate of change of speed with respect to time. When acceleration is constant, as it is in this case, a direct relationship exists between time and the change in speed. However, this relationship is not necessarily a doubling relationship.

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Key Concepts

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

Uniform Acceleration
Uniform acceleration occurs when an object's velocity changes at a constant rate over time. This means that the acceleration, or the rate at which speed increases or decreases, remains the same throughout the period of motion. When an object, like the car in our exercise, starts from rest and speeds up to a certain velocity, it does so by consistently increasing its speed.

In practical terms, understanding uniform acceleration helps predict how long it will take a moving object to reach a certain speed. The formula for uniform acceleration is essential in physics problems, as it describes a linear relationship between velocity change, time, and acceleration:
  • Formula: \( a = \frac{v - u}{t} \)
  • where \( a \) is acceleration, \( v \) is final velocity, \( u \) is initial velocity, and \( t \) is time taken.
Uniform acceleration is an underpinning concept in kinematics that simplifies calculations and interpretations in physics.
Velocity Calculation
Understanding velocity calculation is key to analyzing motion in physics. Velocity tells us both how fast an object is moving and in which direction. To calculate the change in velocity when there's uniform acceleration, we need to focus on initial and final velocity values.

Velocity calculation often starts with the formula for acceleration we explored earlier. Given that you know the acceleration and initial velocity, you can determine how the velocity changes over time:
  • The formula: \( v = u + at \)
  • where \( v \) is final velocity, \( u \) is initial velocity, \( a \) is acceleration, and \( t \) is the time of travel.
In our exercise, calculating the velocity change from 10.0 m/s to 20.0 m/s involves knowing the constant acceleration. With this, we rearrange the basic acceleration formula to find the time it takes for this speed change under uniform acceleration, proving how each velocity value fits into the context of uniform change.
Time-Velocity Relationship
The time-velocity relationship in a scenario of uniform acceleration is straightforward yet significant. It describes how the velocity of an object changes linearly over time when the object moves with a constant acceleration.

A critical point from our exercise is that doubling the time doesn't necessarily mean the velocity doubles as well. This misconception often arises from misunderstanding how acceleration integrates time and velocity.
  • When acceleration \( a \) is constant, the change in velocity \( \Delta v \) can be expressed as \( \Delta v = a \, t\).
  • If time \( t \) doubles, the change in velocity is simply \( a \, (2t) \), meaning it is proportional to time but not an automatic doubling of initial parameters.
Thus, while there is a direct, proportional relationship between time and velocity change when considering uniform acceleration, it is vital to distinguish between simple proportionality and specific outcomes like doubling.

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Most popular questions from this chapter

A student throws a set of keys vertically upward to his fraternity brother, who is in a window a distance \(h\) above. The brother's outstretched hand catches the keys on their way up a time \(t\) later. (a) With what initial velocity were the keys thrown? (b) What was the velocity of the keys just before they were caught? (Answers should be in terms of \(h, g\), and \(t .)\)

A tennis player tosses a tennis ball straight up and then catches it after \(2.00 \mathrm{~s}\) at the same height as the point of release. (a) What is the acceleration of the ball while it is in flight? (b) What is the velocity of the ball when it reaches its maximum height? Find (c) the initial velocity of the ball and (d) the maximum height it reaches.

A certain cable car in San Francisco can stop in \(10 \mathrm{~s}\) when traveling at maximum speed. On one oceasion, the driver sees a dog a distance \(d \mathrm{~m}\) in front of the car and slams on the brakes instantly. The car reaches the dog \(8.0 \mathrm{~s}\) later, and the dog jumps off the track just in time. If the car travels \(4.0 \mathrm{~m}\) beyond the position of the dog before coming to a stop, how far was the car from the dog? (Hint: You will need three equations.)

A record of travel along a straight path is as follows: 1\. Start from rest with a constant acceleration of \(2.77 \mathrm{~m} / \mathrm{s}^{2}\) for \(15.0 \mathrm{~s}\) 2\. Maintain a constant velocity for the nexL \(2.05 \mathrm{~min}\). 3\. Apply a constant negative acceleration of \(-9.47 \mathrm{~m} / \mathrm{s}^{2}\) for \(4.39 \mathrm{~s}\). (a) What was the total displacement for the trip? (b) What were the average speeds for legs 1,2, and 3 of the trip, as well as for the complete trip?

A speedboat increases its speed uniformly from \(v_{t}=\) \(20.0 \mathrm{~m} / \mathrm{s}\) to \(v_{j}=30.0 \mathrm{~m} / \mathrm{s}\) in a distance of \(2.00 \times 10^{2} \mathrm{~m}\) (a) Draw a coordinate system for this situation and label the relevant quantities, including vectors. (b) For the given information, what single equation is most appropriate for finding the acceleration? (c) Solve the equation selected in part (b) symbolically for the boat's acceleration in terms of \(v_{f}, v_{a}\), and \(\Delta x\). (d) Substitute given values, obtaining that acceleration. (e) Find the time it takes the boat to travel the given distance.

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