Answer:

Explanation:
For n-=1 state hydrogen energy level is split into three componets in the presence of external magnetic field. The energies are,
,
,

Here, E is the energy in the absence of electric field.
And
are the highest and the lowest energies.
The difference of these energies

is known as Bohr's magneton.
B=2.5 T,
Therefore,

Now,

Therefore, the energy difference between highest and lowest energy levels in presence of magnetic field is 
Answer:
B.The force of friction between the block and surface will decrease.
Explanation:
The force of friction is given by

where
is the coefficient of friction and
is the normal force.
When the student pulls on the block with force
at an angle
, the normal force on the block becomes

and hence the frictional force becomes
.
Now, as we increase
,
increases which as a result decreases the normal force
, which also means the frictional force decreases; Hence choice B stands true.
<em>P.S: Choice D is tempting but incorrect since the weight </em>
<em> is independent of the external forces on the block. </em>
Answer:
Mechanical advantage = 3
Explanation:
You exert a 100-N force on a pulley system to lift 300-N.
The mechanical advantage of the system is given by the ratio of output force to the input force.
Here, output force = 300 N and input force = 100 N
Mechanical advantage,

Mechanical advantage is 3 it means that there are 3 sections of rope support. Hence, this is the required solution.
Answer:

Explanation:
Given
Mass = 10kg
Velocity = 2m/s
Required
Calculate the momentum of the man
Momentum is calculated as thus
or

So; to solve this question; we simply substitute 10kg for mass and 2m/s for velocity in the above formula;
The formula becomes



Hence, the momentum of the man is 
The bar magnet and the electromagnet act identical. The difference being a electromagnet is a coil of wire that has a power source connect to both ends, this energizes the coil with an electromagnetic field.