Answer:
This is an incomplete question. The complete question is --
An individual white LED (light-emitting diode) has an efficiency of 20% and uses 1.0 W of electric power.
How many LEDs must be combined into one light source to give a total of 3.8W of visible-light output (comparable to the light output of a 100W incandescent bulb)?
And the answer is --
19 LEDs
Explanation:
The full form of LED is Light emitting diode.
It is given that the efficiency of the LED bulb is 20 %
1 LED uses power = 1 W
So the output power of 1 LED = 0.2 W
We need to find the power required to give a 3.8 W light.
Power required for 3.8 W = Number of LEDs required = (total required power / power required for 1 LED )
= 3.8 / 0.2
= 19
Therefore, the number of LEDs required is 19.
Answer:
24.2 m/s
Explanation:
The stone strikes the ground at an angle of 45 degrees: this means that its vertical velocity is equal (in magnitude) to its horizontal velocity, in fact:
The motion along the vertical direction is a uniformly accelerated motion, so we can find the final vertical velocity using the following suvat equation
where
is the final vertical velocity
is the initial vertical velocity (zero because the stone is thrown horizontally)
is the acceleration of gravity (we take downward as positive direction)
s = 30 m is the vertical displacement
Solving for vy,
This means that the horizontal velocity is also 24.2 m/s: and since the horizontal velocity is constant during the whole motion (there is no acceleration in the horizontal direction), this means that the stone was thrown exactly at 24.2 m/s.
In water, it's drag. Exactly the same as air resistance
only hundreds of times greater.
Answer:
The acceleration is: 
Explanation:
Recall that acceleration is defined as the change of velocity over the time it took to produce this change. This is expressed mathematically as:
with 
being the initial velocity of the person (in our case 4 m/s);
being his final velocity (in our case 15 m/s);
and the difference 
the time the change in velocity took (in our case 1 second).
Therefore in our example, the person's acceleration is:
