Math Problem Statement

If a cliff is 5.48 meters tall, How long (in s) would it take to reach the ground if it is thrown straight down at a velocity of 8.17 m/s

Solution

To find the time it takes for an object thrown straight down to reach the ground, we can use the following kinematic equation:

s=v0t+12at2s = v_0 t + \frac{1}{2} a t^2

where:

  • ss is the distance (5.48 meters),
  • v0v_0 is the initial velocity (8.17 m/s),
  • aa is the acceleration due to gravity (approximately 9.81 m/s²),
  • tt is the time in seconds.

Rewriting the equation:

5.48=8.17t+129.81t25.48 = 8.17 t + \frac{1}{2} \cdot 9.81 \cdot t^2

This simplifies to:

5.48=8.17t+4.905t25.48 = 8.17 t + 4.905 t^2

This is a quadratic equation in the form:

4.905t2+8.17t5.48=04.905 t^2 + 8.17 t - 5.48 = 0

To solve for tt, we use the quadratic formula:

t=b±b24ac2at = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

Here, a=4.905a = 4.905, b=8.17b = 8.17, and c=5.48c = -5.48.

Plugging in the values:

t=8.17±(8.17)244.905(5.48)24.905t = \frac{-8.17 \pm \sqrt{(8.17)^2 - 4 \cdot 4.905 \cdot (-5.48)}}{2 \cdot 4.905}

t=8.17±66.7489+107.33289.81t = \frac{-8.17 \pm \sqrt{66.7489 + 107.3328}}{9.81}

t=8.17±174.08179.81t = \frac{-8.17 \pm \sqrt{174.0817}}{9.81}

t=8.17±13.19259.81t = \frac{-8.17 \pm 13.1925}{9.81}

This gives us two solutions:

t1=8.17+13.19259.815.02259.810.512secondst_1 = \frac{-8.17 + 13.1925}{9.81} \approx \frac{5.0225}{9.81} \approx 0.512 \, \text{seconds}

t2=8.1713.19259.8121.36259.812.178secondst_2 = \frac{-8.17 - 13.1925}{9.81} \approx \frac{-21.3625}{9.81} \approx -2.178 \, \text{seconds}

Since time cannot be negative, we discard t2t_2.

Therefore, the time it takes to reach the ground is approximately:

t0.512secondst \approx 0.512 \, \text{seconds}

Would you like further details or have any questions?

Here are 5 numbered questions you might ask:

  1. How do you derive the kinematic equations used in physics?
  2. Can you explain more about solving quadratic equations?
  3. What assumptions are made in this type of problem?
  4. How does air resistance affect the time to reach the ground?
  5. Can you show the step-by-step process of using the quadratic formula?

Tip: Always check the units of your given values to ensure they are consistent before performing calculations.

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Math Problem Analysis

Mathematical Concepts

Kinematics
Quadratic Equations

Formulas

Kinematic equation
Quadratic formula

Theorems

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Suitable Grade Level

Grades 10-12