/*! 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 47 A semitrailer is coasting downhi... [FREE SOLUTION] | 91Ó°ÊÓ

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A semitrailer is coasting downhill along a mountain highway when its brakes fail. The driver pulls onto a runaway-truck ramp that is inclined at an angle of \(14.0^{\circ}\) above the horizontal. The semitrailer coasts to a stop after traveling \(154 \mathrm{m}\) along the ramp. What was the truck's initial speed? Neglect air resistance and friction.

Short Answer

Expert verified
The truck's initial speed was approximately 23.7 m/s.

Step by step solution

01

Determine Deceleration Due to Gravity

The truck decelerates due to gravity acting along the ramp. The component of gravitational acceleration along the ramp is given by \( g \sin(\theta) \), where \( g = 9.81 \ m/s^2 \) is the acceleration due to gravity, and \( \theta = 14.0^{\circ} \) is the angle of the ramp. Calculate this component: \( a = 9.81 \sin(14.0^{\circ}) \).
02

Apply Kinematic Equation

Use the kinematic equation \( v^2 = u^2 + 2as \), where \( v \) is the final velocity (0 m/s, as the truck comes to a stop), \( u \) is the initial velocity, \( a \) is the acceleration (calculated in Step 1 but negative), and \( s = 154 \ m \) is the distance traveled along the ramp. Rearrange for \( u \): \( u = \sqrt{-2as} \).
03

Calculate Initial Speed

Substitute the values into the rearranged kinematic equation to find \( u \). First, calculate the deceleration \( a \) obtained from Step 1. Then, calculate \( u = \sqrt{-2(-9.81 \sin(14.0^{\circ}) \times 154)} \).
04

Compute Result

Perform the calculation and find \( u \). The initial speed of the truck is approximately \( 23.7 \ m/s \).

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Key Concepts

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

Deceleration
Deceleration is a term used to describe a reduction in speed or velocity over time. In physics, when discussing motion along a straight path, deceleration is often associated with negative acceleration. It's important to remember that acceleration and deceleration are essentially the same concept, but with acceleration, the speed increases, and with deceleration, it decreases.
In the scenario of the runaway truck on the incline, deceleration is caused by the component of gravitational force acting parallel to the inclined ramp. This force opposes the truck's initial motion. To calculate this component, we use the sine of the incline's angle. This gives us:
  • The gravitational force component is calculated as: \( a = g \sin(\theta) \)
  • Here, \( g = 9.81 \, \text{m/s}^2 \) is the standard gravitational acceleration.
  • \( \theta = 14.0^{\circ} \) represents the angle of the ramp.
This equation yields the deceleration along the ramp, which is essential for determining the truck's motion dynamics.
Gravitational Acceleration
Gravitational acceleration is the rate at which an object's velocity changes due to the force of gravity. On Earth's surface, this is standardized to \( g = 9.81 \, \text{m/s}^2 \). This force pulls objects toward the Earth's center, influencing any motion by altering speeds—speeding up or slowing down—in the absence of other forces.
In the example of the runaway truck, the gravitational acceleration plays a critical role as it is directed downwards through the inclined ramp. When dealing with slopes or ramps, gravitational acceleration isn't directly vertical. Instead, it's divided into two components: one parallel and one perpendicular to the inclined plane.
  • The parallel component, \( g \sin(\theta) \), causes the truck to decelerate as it moves up the ramp.
  • It's crucial for calculating how gravity influences object motion along slanted surfaces.
Understanding gravitational acceleration and its components helps predict object behavior in similar physical setups.
Kinematic Equations
Kinematic equations are a series of mathematical formulas used to calculate aspects of an object's motion, such as velocity, acceleration, time, and displacement. These equations apply only under constant acceleration, making them particularly useful in physics problems like the one with the truck on a ramp.
The primary kinematic equation used in our scenario is:
  • \( v^2 = u^2 + 2as \)
  • Where \( v \) is the final velocity (0 m/s, since the truck stops), \( u \) is the initial velocity we wish to determine, \( a \) is the constant acceleration (or deceleration), and \( s \) is the distance traveled [154 m in this case].
By rearranging and substituting the known values into the equation, we solve for \( u \), the truck's initial speed. This technique helps identify various motion characteristics in physics and solves real-world motion problems effectively.

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Most popular questions from this chapter

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