/*! 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 38 You throw a glob of putty straig... [FREE SOLUTION] | 91Ó°ÊÓ

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You throw a glob of putty straight up toward the ceiling, which is 3.60 \(\mathrm{m}\) above the point where the putty leaves your hand. The initial speed of the putty as it leaves your hand is 9.50 \(\mathrm{m} / \mathrm{s}\). (a) What is the speed of the putty just before it strikes the ceiling? (b) How much time from when it leaves your hand does it take the putty to reach the ceiling?

Short Answer

Expert verified
(a) 4.44 m/s (b) 0.516 seconds

Step by step solution

01

Identify Known Values

First, we list the given values from the problem for clarity. The initial speed (\(v_i\)) is \(9.50 \, \mathrm{m/s}\). The displacement (\(s\)) is \(3.60 \, \mathrm{m}\). The acceleration (\(a\)) due to gravity is \(-9.81 \, \mathrm{m/s}^2\) (negative because it acts downwards).
02

Apply Kinematic Equation for Final Speed (Part a)

To find the final speed (\(v_f\)) of the putty just before it hits the ceiling, we use the kinematic equation: \[ v_f^2 = v_i^2 + 2as \]Substitute the known values:\[ v_f^2 = (9.50)^2 + 2(-9.81)(3.60) \]Calculate:\[ v_f^2 = 90.25 - 70.488 \]\[ v_f^2 = 19.762 \]Take the square root:\[ v_f = \sqrt{19.762} \approx 4.44 \, \mathrm{m/s} \]
03

Use Kinematic Equation to Find Time (Part b)

We need to find the time (\(t\)) it takes for the putty to reach the ceiling. We use the equation: \[ v_f = v_i + at \]Re-arrange to solve for \(t\): \[ t = \frac{v_f - v_i}{a} \]Substitute the values computed and known:\[ t = \frac{4.44 - 9.50}{-9.81} \]Calculate:\[ t \approx \frac{-5.06}{-9.81} \approx 0.516 \] seconds.

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Key Concepts

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

Projectile Motion
Projectile motion involves any object propelled into the air and influenced only by gravity, assuming air resistance is negligible. This encompasses familiar examples like a ball being tossed or a stone skipped across water. The main motion occurs in a predictable parabolic path caused primarily by the gravitational pull downward. In the context of our problem, the putty behaves like a projectile, thrown vertically into the air toward a ceiling.

Two key components are involved in understanding projectile motion:
  • Vertical Motion: The force of gravity impacts the motion vertically, providing a constant acceleration downwards, measured as approximately \(9.81 \, \mathrm{m/s^2}\).
  • Initial Velocity: The launch velocity directs how high and fast the projectile will move initially. In our scenario, the putty is launched upwards with an initial velocity of \(9.50 \, \mathrm{m/s}\).

Recognizing these components allows you to calculate parameters like maximum height, time to reach a peak, and speed upon impact with the ceiling. Understanding projectile motion aids in visualizing how forces interact with objects in flight.
Kinematic Equations
Kinematic equations are fundamental tools in physics that describe motion in terms of velocity, acceleration, displacement, and time. They apply in situations with constant acceleration, like our throw of putty at the ceiling. Let's revisit the two equations from the exercise and how they are crucial.

  • Final Speed Calculation: The equation \( v_f^2 = v_i^2 + 2as \) helps determine the final speed of the projectile just before it hits the ceiling. The equation encompasses initial velocity \(v_i\), acceleration \(a\), and displacement \(s\), showing how each factor contributes to the viability of motion.
  • Time to Reach Ceiling: To find how long the putty takes to hit the ceiling, we use \( v_f = v_i + at \). By rearranging, it provides a measure of time \(t\) using the input of final velocity \(v_f\), initial velocity \(v_i\), and acceleration \(a\).


The elegance of kinematic equations lies in their simplicity and power, helping solve motion problems quickly. For our exercise, they involve substitution of known values to yield precise, predictable results.
Physics Problem Solving
Mastering physics problem-solving techniques allows you to systematically approach and accurately solve complex physics scenarios. For our problem involving the putty's projectile motion, several strategic steps are involved in solving it effectively:

  • Clarify Known Quantities: Document all given values like initial speed, displacement, and acceleration. These provide the foundational data required for further calculations.
  • Select Appropriate Equations: Choose kinematic equations that directly relate the variables you aim to find. The selected equations must align with the quantities and unknowns presented in the problem.
  • Execute Calculations: Substitute the known values into equations, carefully perform mathematical operations, and solve for unknowns. Take caution with signs, especially when dealing with acceleration, which can be negative in the direction of gravity.
  • Review and Verify Results: Double-check calculations and ensure units align consistently, and confirm results are logical given the context of motion and physics laws.

By following these structured steps, solving physics problems becomes less daunting, fostering confidence and a deeper understanding of physical principles at play.

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Most popular questions from this chapter

A ball starts from rest and rolls down a hill with uniform acceleration, traveling 150 \(\mathrm{m}\) during the second 5.0 \(\mathrm{s}\) of its motion. How far did it roll during the first 5.0 s of motion?

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A world-class sprinter accelerates to his maximum speed in 4.0 s. He then maintains this speed for the remainder of a \(100-\mathrm{m}\) race, finishing with a total time of 9.1 \(\mathrm{s}\) . (a) What is the runner's average acceleration during the first 4.0 \(\mathrm{s} ?\) (b) What is his average acceleration during the last 5.1 \(\mathrm{s} ?\) (c) What is his average acceleration for the entire race? (d) Explain why your answer to part (c) is not the average of the answers to parts (a) and (b).

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