Answer:
Rutherford described the atom as consisting of a tiny positive mass surrounded by a cloud of negative electrons. Bohr thought that electrons orbited the nucleus in quantised orbits. Bohr built upon Rutherford's model of the atom. ... So it was not possible for electrons to occupy just any energy level.
Explanation:
Answer: (B) There is complete destructive interference between the incoming and reflected waves
Explanation:
For example, if you pluck a guitar the waves will travel back and forth. They consist of nodes and anti-nodes. It is created, when the wave traveling to one side and bounces of the other end and comes back. As it travels to the other side, it is reflected thus, comes back. So standing waves occurs when there is interference.
When the wave is produced, the points where the string is not moving are called nodes and where they are moving are called anti-nodes. The positions where nodes are produced, destructive interference occurs and where anti-nodes are produced, constructive interference occurs
The work done on the sail is 600 J
Explanation:
The work done to lift the sail is equal to the gain in gravitational potential energy of the sail, therefore is:

where
m is the mass of the sail
g is the acceleration of gravity
(mg) is the weight of the sail
is the change in height of the sail
In this problem we have
mg = 150 N (weight)

Substituting, we find the work done:

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The work done by the gravitational force = 0
Given the mass of the box = 40 kg
The box is initially at rest.
Distance moved by the applied force = 5m
Force applied = 130 N
Co-efficient of friction between the box and floor = 0.3
The box is moved only in the horizontal direction by the applied force.
Gravitational force is applied in a direction perpendicular to the applied force. hence it doesn't do any work on the box.
Therefore, the work done by the gravitational force is zero.
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