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At a carnival, you can try to ring a bell by striking a target with a \(9.00-\mathrm{kg}\) hammer. In response, a \(0.400-\mathrm{kg}\) metal piece is sent upward toward the bell, which is \(5.00 \mathrm{m}\) above. Suppose that \(25.0 \%\) of the hammer's kinetic energy is used to do the work of sending the metal piece upward. How fast must the hammer be moving when it strikes the target so that the bell just barely rings?

Short Answer

Expert verified
The hammer must be moving at approximately 4.18 m/s.

Step by step solution

01

Understand the Problem

We need to find the velocity of the hammer required to just barely ring a bell that is 5.00 m above. Only 25% of the hammer's kinetic energy is used to propel a 0.400 kg metal piece upward.
02

Relate Kinetic Energy to Height

To ring the bell, the potential energy at the height (5.00 m) must be equal to the portion of kinetic energy transferred (25% of the hammer's kinetic energy): \[ KE_{metal} = PE_{max}\]where \( KE_{metal} = 0.25 imes KE_{hammer} \) and \( PE_{max} = mgh \) for the metal piece. Here, \( m = 0.400 \, \text{kg} \), \( g = 9.81 \, \text{m/s}^2 \), and \( h = 5.00 \, \text{m} \).
03

Calculate Potential Energy at Maximum Height

The potential energy needed for the metal to reach 5.00 m is:\[PE_{max} = mgh = 0.400 \, \text{kg} \times 9.81 \, \text{m/s}^2 \times 5.00 \, \text{m}\]\[PE_{max} = 19.62 \, \text{J}\]
04

Relate with Hammer's Kinetic Energy

Since only 25% of the hammer's kinetic energy is used:\[0.25 imes KE_{hammer} = 19.62 \, \text{J}\]
05

Calculate Hammer's Kinetic Energy

Rearrange the equation to find \( KE_{hammer} \):\[KE_{hammer} = \frac{19.62}{0.25} \, \text{J} = 78.48 \, \text{J}\]
06

Find the Hammer's Velocity

Substitute \( KE_{hammer} = \frac{1}{2}mv^2 \) to find the hammer's velocity \( v \):\[78.48 \, \text{J} = \frac{1}{2} \times 9.00 \, \text{kg} \times v^2\]Solve for \( v \):\[v^2 = \frac{78.48}{4.5}\]\[v^2 = 17.44 \]\[v = \sqrt{17.44} \, \text{m/s}\]\[v \approx 4.18 \, \text{m/s}\]

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Key Concepts

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

Energy Conversion
Energy conversion is a fascinating process where energy changes from one form to another. In this exercise, we are looking at how the kinetic energy from the moving hammer is converted into potential energy when the metal piece is propelled upwards. This transformation is crucial at amusement parks or carnivals in games like ringing a bell with a hammer.
In real-world scenarios, not all energy gets perfectly converted. Some of it is lost to other forms like heat or sound.
This loss in conversion efficiency is what we observe in the problem: only 25% of the hammer's kinetic energy is used to propel the metal piece upwards. The art of balancing and maximizing these energy conversions is key in various fields like engineering and environmental science.
Kinetic Energy
Kinetic energy ( \( KE \) ) is the energy an object possesses due to its motion. It depends on two variables: the mass of the object and its velocity. Mathematically, it's expressed as \( KE = \frac{1}{2} m v^2 \).
  • For the hammer in our example, its mass is 9.00 kg.
  • We know that it needs enough velocity to ensure a 25% conversion rate facilitates the bell ringing.
In simpler terms, when you swing the hammer at a target in a carnival game, the energy that powers the metal piece to shoot upwards comes from this kinetic energy derived from both the hammer's mass and speed. The faster you swing, the higher the kinetic energy, and thus the higher the potential energy that can be achieved by the metal block.
Potential Energy
Potential energy ( \( PE \) ) is the energy stored due to an object's position or configuration. In our example, as the metal piece rises to a height of 5m, its potential energy is calculated using \( PE = mgh \).
  • Here,
    • \( m = 0.400 \, \text{kg} \)
    • \( g = 9.81 \, \text{m/s}^2 \)
    • \( h = 5.00 \, \text{m} \)
  • When fully exerted, the potential energy computed to reach the bell is 19.62 J.
All this means that at the height needed to ring the bell, the energy of the piece is converted into potential energy until it stops momentarily at its peak before potentially falling back down.
Conservation of Energy
The principle of conservation of energy states that energy cannot be created or destroyed, only transformed from one form to another. In many physical scenarios, like our carnival game, the total energy remains constant, though it might not appear so due to losses like sound or heat energy at impact points.
In the exercise, once the hammer strikes the target, the system's energy remains constant. Of course, we noted that only 25% of the hammer’s kinetic energy is transmitted upward. Still, the total mechanical energy within the system before and after remains unchanged. Hence, understanding that energy doesn't vanish but merely changes form is crucial in solving energy-related physics problems.

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