Difference between revisions of "Kinetic Energy Store"
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{| class="wikitable" | {| class="wikitable" | ||
| style="height:20px; width:200px; text-align:center;" |A 75kg person has a '''kinetic energy''' of 96J while while walking. Calculate their [[speed]]. | | style="height:20px; width:200px; text-align:center;" |A 75kg person has a '''kinetic energy''' of 96J while while walking. Calculate their [[speed]]. | ||
− | | style="height:20px; width:200px; text-align:center;" | | + | | style="height:20px; width:200px; text-align:center;" |A [[bird]] of [[mass]] 2.4kg flies at a constant [[speed]] with a '''kinetic energy store''' of 1500J. Calculate the [[speed]] of the [[bird]] correct to two [[Significant Figure|significant figures]]. |
| style="height:20px; width:200px; text-align:center;" |Question | | style="height:20px; width:200px; text-align:center;" |Question | ||
|- | |- | ||
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m = 75kg | m = 75kg | ||
| style="height:20px; width:200px; text-align:left;" |'''1. State the known quantities''' | | style="height:20px; width:200px; text-align:left;" |'''1. State the known quantities''' | ||
+ | E<sub>k</sub> = 1500J | ||
+ | |||
+ | m = 2.4kg | ||
| style="height:20px; width:200px; text-align:left;" |'''1. State the known quantities''' | | style="height:20px; width:200px; text-align:left;" |'''1. State the known quantities''' | ||
|- | |- | ||
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| style="height:20px; width:200px; text-align:left;" |'''2. [[Substitute (Maths)|Substitute]] the numbers and [[Evaluate (Maths)|evaluate]].''' | | style="height:20px; width:200px; text-align:left;" |'''2. [[Substitute (Maths)|Substitute]] the numbers and [[Evaluate (Maths)|evaluate]].''' | ||
+ | <math>E_k = \frac{1}{2} m v^2</math> | ||
+ | |||
+ | <math>1500 = \frac{1}{2} \times 2.4 \times v^2</math> | ||
+ | |||
+ | <math>1500 = 1.2v^2</math> | ||
| style="height:20px; width:200px; text-align:left;" |'''2. [[Substitute (Maths)|Substitute]] the numbers and [[Evaluate (Maths)|evaluate]].''' | | style="height:20px; width:200px; text-align:left;" |'''2. [[Substitute (Maths)|Substitute]] the numbers and [[Evaluate (Maths)|evaluate]].''' | ||
|- | |- | ||
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| style="height:20px; width:200px; text-align:left;" |'''3. [[Rearrange (Maths)|Rearrange]] the equation and [[Solve (Maths)|solve]].''' | | style="height:20px; width:200px; text-align:left;" |'''3. [[Rearrange (Maths)|Rearrange]] the equation and [[Solve (Maths)|solve]].''' | ||
+ | |||
+ | <math>v^2 = \frac{1500}{1.2}</math> | ||
+ | |||
+ | <math>v = \sqrt{\frac{1500}{1.2}}</math> | ||
+ | |||
+ | <math>v = 35.35534m/s</math> | ||
+ | |||
+ | <math>v \approx 35m/s</math> | ||
+ | |||
| style="height:20px; width:200px; text-align:left;" |'''3. [[Rearrange (Maths)|Rearrange]] the equation and [[Solve (Maths)|solve]].''' | | style="height:20px; width:200px; text-align:left;" |'''3. [[Rearrange (Maths)|Rearrange]] the equation and [[Solve (Maths)|solve]].''' | ||
|} | |} |
Revision as of 13:12, 31 January 2019
Contents
Key Stage 3
Meaning
The kinetic energy store is the energy store associated with moving objects.
About The Kinetic Energy Store
- The faster an object moves the more energy it has in its kinetic store.
- If two objects are moving at the same speed the one with more mass has more energy in the kinetic store.
Equation
The equation for kinetic energy written in words. |
The equation for kinetic energy written in symbols. |
Calculating Kinetic Energy
A 700kg formula one racing car has a top speed of 100m/s. Calculate the kinetic energy of the car to two significant figures. | A cheetah of mass 75kg runs at a speed of 32m/s. Calculate the kinetic energy of the cheetah correct to two significant figures. | A 160g cricket ball is hit at 44m/s. Calculate the kinetic energy of the cricket ball correct to two significant figures. |
1. State the known quantities
m = 700kg v = 100m/s |
1. State the known quantities
m = 75kg v = 32m/s |
1. State the known quantities
m = 160g min kilograms = \(\frac{160}{1000}\) m = 0.16kg v = 32m/s |
2. Substitute the numbers into the equation and solve.
\(E_k = \frac{1}{2} m v^2\) \(E_k = \frac{1}{2} \times 700 \times 100^2\) \(E_k = \frac{1}{2} \times 700 \times 10,000\) \(E_k = 3,500,000J\) |
2. Substitute the numbers into the equation and solve.
\(E_k = \frac{1}{2} m v^2\) \(E_k = \frac{1}{2} \times 75 \times 32^2\) \(E_k = \frac{1}{2} \times 75 \times 1024\) \(E_k = 38,400J\) \(E_k \approx 38000J\) |
2. Substitute the numbers into the equation and solve.
\(E_k = \frac{1}{2} m v^2\) \(E_k = \frac{1}{2} \times m \times v^2\) \(E_k = \frac{1}{2} \times 0.16 \times 44^2\) \(E_k = \frac{1}{2} \times 0.16 \times 1936\) \(E_k = 154.88J\) \(E_k \approx 150J\) |
Key Stage 4
Meaning
The kinetic energy store is the energy store associated with moving objects.
About Kinetic Energy
- Any moving object stores kinetic energy.
- The kinetic energy store of an object is related to two properties of the object:
- The mass of the object - The greater the mass the greater the kinetic energy stored.
- The speed or velocity of the object - The greater the speed the greater the kinetic energy stored.
Equation
NB: You must memorise this equation!
Kinetic Energy = 0.5 x (Mass) x (Speed)2
\(E_k = \frac{1}{2} m v^2\)
Where:
Ek = Kinetic Energy stored.
v = The speed or velocity of the object.
Calculating Velocity from Kinetic Energy
A 75kg person has a kinetic energy of 96J while while walking. Calculate their speed. | A bird of mass 2.4kg flies at a constant speed with a kinetic energy store of 1500J. Calculate the speed of the bird correct to two significant figures. | Question |
1. State the known quantities
Ek = 96J m = 75kg |
1. State the known quantities
Ek = 1500J m = 2.4kg |
1. State the known quantities |
2. Substitute the numbers and evaluate.
\(E_k = \frac{1}{2} m v^2\) \(96 = \frac{1}{2} \times 75 \times v^2\) \(96 = 37.5v^2\) |
2. Substitute the numbers and evaluate.
\(E_k = \frac{1}{2} m v^2\) \(1500 = \frac{1}{2} \times 2.4 \times v^2\) \(1500 = 1.2v^2\) |
2. Substitute the numbers and evaluate. |
3. Rearrange the equation and solve.
\(v^2 = \frac{96}{37.5}\) \(v = \sqrt{\frac{96}{37.5}}\) \(v = 1.6m/s\) |
3. Rearrange the equation and solve.
\(v^2 = \frac{1500}{1.2}\) \(v = \sqrt{\frac{1500}{1.2}}\) \(v = 35.35534m/s\) \(v \approx 35m/s\) |
3. Rearrange the equation and solve. |