Answer:
B) A stack of books is carried at waist level across a room
Explanation:
Work is defined as:
where
F is the force applied
d is the displacement of the object
is the angle between the direction of the force and of the displacement
From the formula, we see that the work done is zero when the force and the displacement are perpendicular to each other. Let's now analyze each situation:
A) A bookcase is slid across carpeting. --> work is done, because the force that pushes the bookcase is in the same direction of the displacement
B) A stack of books is carried at waist level across a room. --> no work is done, because the force to carry the book is vertical, while the displacement of the books is horizontal
C) A chair is lifted vertically with respect to the floor. --> work is done, because the force that lifts the chair is vertical, and the displacement is vertical as well
D) A table is dropped onto the ground. --> work is done, because the force of gravity (that makes the table falling down) is vertical and the displacement of the table is also vertical.
Answer:
Centre of mass is the point at which the distribution of mass is equal in all directions, and does not depend on gravitational field. Centre of gravity is the point at which the distribution of weight is equal in all directions, and does depend on gravitational field.
Answer:
Since incident wave and its reflected part in opposite phase superimpose on each other
So correct answer will be
Option B
Explanation:
Here we know that the wave reflection is done by rigid boundary
So when wave is reflected by the boundary then its phase is reversed by 180 degree
so the reflected wave is in reverse phase from the boundary
so we can superimpose the reflected part with incident wave to dine the resultant wave
So the phenomenon is given as follow
(a) 10 GHz is the frequency of microwave radiation.
(b) 0.167 ms is required by the microwave to travel between two mountains.
Answer:
Explanation:
(a). 1 MHz is the frequency of microwave radiation.
(b) 0.167 ms is required by the microwave to travel between two mountains.
Answer:
Explanation:
a. Frequency is the measure of number of times a same thing will be repeated in a given time interval for a given time. And wavelength is the measure of distance between two successive crests or troughs. So wavelength and frequency are inversely proportional to each other. And velocity of light is the proportionality constant.
So frequency of microwave radiation = Speed of light/Wavelength of radiation
Frequency = 
Frequency = 
So 10 GHz is the frequency of microwave radiation.
b). As microwave is a part of light waves, so it will be experiencing the speed of light.
As the speed is 3*
m/s and the distance between the two mountains is given as 50 km, then time can be calculated as
Time = Distance/Velocity
Time = 
So time = 0.167 ms.
Thus, 0.167 ms is required by the microwave to travel between two mountains.
