Math Problem Statement

A coin is dropped from the top of a building that is 1,310 feet tall. Use the position function below for free-falling objects. s(t) = −16t2 + v0t + s0 (a) Determine the position and velocity functions for the coin. s(t) =

Incorrect: Your answer is incorrect. v(t) =

Incorrect: Your answer is incorrect. (b) Determine the average velocity (in ft/s) on the interval [3, 4]. -112

Correct: Your answer is correct. ft/s (c) Find the instantaneous velocities (in ft/s) when t = 3 seconds and t = 4 seconds. v(3) = -96

Correct: Your answer is correct. ft/s v(4) = -128

Correct: Your answer is correct. ft/s (d) Find the time (in s) required for the coin to reach the ground level. (Round your answer to three decimal places.) t =

Incorrect: Your answer is incorrect. s (e) Find the velocity (in ft/s) of the coin at impact. (Round your answer to one decimal place.)

Incorrect: Your answer is incorrect. ft/s

Solution

Let's work through each part of the problem step by step.

Part (a): Position and velocity functions

The given position function for a free-falling object is:

s(t)=16t2+v0t+s0s(t) = -16t^2 + v_0t + s_0

where:

  • s(t)s(t) is the position at time tt (in feet),
  • v0v_0 is the initial velocity (in ft/s),
  • s0s_0 is the initial height (in feet),
  • and tt is the time (in seconds).

For this problem:

  • The coin is dropped from a height of 1,310 feet, so the initial velocity v0=0v_0 = 0 ft/s (because it's dropped, not thrown).
  • The initial height s0=1310s_0 = 1310 feet.

Thus, the position function becomes:

s(t)=16t2+1310s(t) = -16t^2 + 1310

To find the velocity function, we differentiate the position function with respect to tt:

v(t)=ddt(16t2+1310)=32tv(t) = \frac{d}{dt} \left( -16t^2 + 1310 \right) = -32t

So:

  • The position function is s(t)=16t2+1310s(t) = -16t^2 + 1310,
  • The velocity function is v(t)=32tv(t) = -32t.

Part (b): Average velocity on the interval [3, 4]

The average velocity vavg\text{v}_{\text{avg}} on the interval [a,b][a, b] is given by:

vavg=s(b)s(a)ba\text{v}_{\text{avg}} = \frac{s(b) - s(a)}{b - a}

For the interval [3,4][3, 4]:

  1. Find s(3)s(3) and s(4)s(4): s(3)=16(3)2+1310=144+1310=1166feets(3) = -16(3)^2 + 1310 = -144 + 1310 = 1166 \, \text{feet} s(4)=16(4)2+1310=256+1310=1054feets(4) = -16(4)^2 + 1310 = -256 + 1310 = 1054 \, \text{feet}

  2. Calculate the average velocity: vavg=1054116643=1121=112ft/s\text{v}_{\text{avg}} = \frac{1054 - 1166}{4 - 3} = \frac{-112}{1} = -112 \, \text{ft/s}

This is correct as provided in the problem.


Part (c): Instantaneous velocity at t=3t = 3 and t=4t = 4

The instantaneous velocity is given by the velocity function v(t)=32tv(t) = -32t.

For t=3t = 3: v(3)=32(3)=96ft/sv(3) = -32(3) = -96 \, \text{ft/s}

For t=4t = 4: v(4)=32(4)=128ft/sv(4) = -32(4) = -128 \, \text{ft/s}

These are also correct as provided.


Part (d): Time to reach the ground

To find the time when the coin reaches the ground, set s(t)=0s(t) = 0 (since the ground level is at height 0):

16t2+1310=0-16t^2 + 1310 = 0

Solve for tt:

16t2=131016t^2 = 1310 t2=131016=81.875t^2 = \frac{1310}{16} = 81.875 t=81.8759.049secondst = \sqrt{81.875} \approx 9.049 \, \text{seconds}

Thus, the time required for the coin to reach the ground is approximately t9.049t \approx 9.049 seconds.


Part (e): Velocity at impact

To find the velocity at impact, use the velocity function v(t)=32tv(t) = -32t, and substitute t=9.049t = 9.049:

v(9.049)=32(9.049)289.6ft/sv(9.049) = -32(9.049) \approx -289.6 \, \text{ft/s}

Thus, the velocity at impact is approximately 289.6ft/s-289.6 \, \text{ft/s}.


Summary of Results

  • Position function: s(t)=16t2+1310s(t) = -16t^2 + 1310
  • Velocity function: v(t)=32tv(t) = -32t
  • Average velocity on [3, 4]: 112ft/s-112 \, \text{ft/s}
  • Instantaneous velocities:
    • v(3)=96ft/sv(3) = -96 \, \text{ft/s}
    • v(4)=128ft/sv(4) = -128 \, \text{ft/s}
  • Time to reach the ground: t9.049secondst \approx 9.049 \, \text{seconds}
  • Velocity at impact: v289.6ft/sv \approx -289.6 \, \text{ft/s}

Would you like further clarification or details on any part?

Here are 5 related questions you could explore:

  1. What would happen if the initial velocity wasn't zero?
  2. How would air resistance affect the results?
  3. What is the physical meaning of negative velocity in this problem?
  4. Can we determine the maximum height if the coin were thrown upwards instead of dropped?
  5. How does the time to fall change if the height is doubled?

Tip: When solving for time in quadratic equations, always consider both positive and negative roots, but remember that negative time is not physically meaningful in this context!

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Math Problem Analysis

Mathematical Concepts

Quadratic Functions
Kinematics
Instantaneous and Average Velocity

Formulas

Position function for free-falling objects: s(t) = -16t^2 + v0t + s0
Velocity function: v(t) = ds/dt = -32t
Average velocity: v_avg = (s(b) - s(a)) / (b - a)
Solving quadratic equations for time: t^2 = s0 / 16

Theorems

Differentiation of quadratic functions
Basic kinematics equation for free fall

Suitable Grade Level

Grades 10-12