How much does it cost to operate a 25-w soldering iron for 8.0 hours if energy costs 8.0¢/kwh?
1 answer:
The power P is defined as the energy E per unit of time t:
In our problem, the power is P=25 W and the total time is t=8.0h, so we can calculate the total energy used during this time:
The energy costs 8€ per each kwh, so we can write the following proportion:
where x is the price corresponding to 0.2 kWh. Solving the proportion we find x:
€
In our problem, the power is P=25 W and the total time is t=8.0h, so we can calculate the total energy used during this time:
The energy costs 8€ per each kwh, so we can write the following proportion:
where x is the price corresponding to 0.2 kWh. Solving the proportion we find x:
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The correct answer to the question is : 29.88 m.
EXPLANATION :
As per the question, the mass of the rock m = 50 Kg.
The rock is rolling off the edges of the cliff.
The final velocity of the rock when it hits the ground v = 24 .2 m/s.
Let the height of the cliff is h.
The potential energy gained by the rock at the top of the cliff = mgh.
Here, g is known as acceleration due to gravity, and g =
When the rock rolls off the edge of the cliff, the potential energy is converted into kinetic energy.
When the rock hits the ground, whole of its potential energy is converted into its kinetic energy.
The kinetic energy of the rock when it touches the ground is given as -
Kinetic energy K.E = .
From above we know that -
Kinetic energy at the bottom of the cliff = potential energy at a height h
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Hence, the height of the cliff is 29.88 m