You saw in 3rd ESO that an object has energy because it is moving or because it is at a height. Before moving on to energy transfers (the next unit), it is worth reviewing this precisely, because you will need it for everything that follows: from a skater going down a ramp to a hydroelectric power station.
Before you start, make sure you know: Converting units (2nd ESO)
If a tennis ball thrown gently hits you, you hardly notice it, but at $150\text{ km/h}$ it can hurt you: how do we quantify the energy due to the movement of an object?
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Kinetic energy is calculated as $E_c = \frac{1}{2} \cdot m \cdot v^2$. A volleyball of $0,3\ \text{kg}$ reaches the player's hands at $24\ \text{m/s}$. Calculate its…
Kinetic energy is calculated as $E_c = \frac{1}{2} \cdot m \cdot v^2$. A volleyball of $0,3\ \text{kg}$ reaches the player's hands at $24\ \text{m/s}$. Calculate its kinetic energy.
A boy and his scooter have a combined mass of $60\ \text{kg}$ and travel at $18\ \text{km/h}$. a) Express the speed in $\text{m/s}$. b) Calculate their kinetic energy.
A boy and his scooter have a combined mass of $60\ \text{kg}$ and travel at $18\ \text{km/h}$.
A flowerpot resting on the ground is no danger at all, but that same pot on the railing of a fifth-floor flat stores a great capacity to break things if it falls: what does that stored energy depend on?
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Potential energy is calculated as $E_p = m \cdot g \cdot h$. A lamp of $3\ \text{kg}$ hangs from the ceiling $2,5\ \text{m}$ above the floor (take…
Potential energy is calculated as $E_p = m \cdot g \cdot h$. A lamp of $3\ \text{kg}$ hangs from the ceiling $2,5\ \text{m}$ above the floor (take $g = 9,8\ \text{m/s}^2$). Calculate its potential energy.
A bag hanging from a peg, $2\ \text{m}$ above the ground, has a potential energy of $140\ \text{J}$ (take $g = 10\ \text{m/s}^2$). What is the mass of the bag? Rearrange…
A bag hanging from a peg, $2\ \text{m}$ above the ground, has a potential energy of $140\ \text{J}$ (take $g = 10\ \text{m/s}^2$). What is the mass of the bag? Rearrange the potential energy formula to solve for mass first.
A plane flies at high speed and at the same time thousands of metres above the ground: how do we measure the total energy that combines both its movement and its altitude?
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State what type of mechanical energy each object has (kinetic, potential, or both) and how it is changing: a) A funicular railway ascending at a constant speed. b) A…
State what type of mechanical energy each object has (kinetic, potential, or both) and how it is changing:
a) A funicular railway ascending at a constant speed.
b) A diver standing still on the diving board before jumping.
A toy helicopter of $0,8\ \text{kg}$ flies at $3\ \text{m/s}$ at a height of $10\ \text{m}$ (take $g = 10\ \text{m/s}^2$), as shown in the figure. a) Calculate its…
A toy helicopter of $0,8\ \text{kg}$ flies at $3\ \text{m/s}$ at a height of $10\ \text{m}$ (take $g = 10\ \text{m/s}^2$), as shown in the figure.
Complete the sentence with the missing words: "The mechanical energy of an object is the $\dots$ of its $\dots$ energy and its $\dots$ energy". Then give an example of…
Complete the sentence with the missing words: "The mechanical energy of an object is the $\dots$ of its $\dots$ energy and its $\dots$ energy". Then give an example of an object that has both types of energy at the same time.
A cat of $4\ \text{kg}$ is sitting on top of a wall and its potential energy relative to the ground is $196\ \text{J}$ (take $g = 9,8\ \text{m/s}^2$). How high is the…
A cat of $4\ \text{kg}$ is sitting on top of a wall and its potential energy relative to the ground is $196\ \text{J}$ (take $g = 9,8\ \text{m/s}^2$). How high is the wall?
A football of $0,45\ \text{kg}$ bounces off at $40\ \text{m/s}$. a) Calculate its kinetic energy. b) At what speed would an athlete of $80\ \text{kg}$ have to run to…
A football of $0,45\ \text{kg}$ bounces off at $40\ \text{m/s}$.
a) Calculate its kinetic energy.
b) At what speed would an athlete of $80\ \text{kg}$ have to run to have the same kinetic energy? Rearrange the formula for speed first.
Back to the beginning: The water held in the hydroelectric power station's reservoir, or the skater at the top of the ramp, store potential energy ($E_p$), which is transformed into kinetic energy ($E_c$) of movement as they descend.
Summary
Let's practice! 8 medium exercises in this section