The frictional force is too much compared to the gravitational force
Explanation:
This is because of the great amount of frictional force between the book and the wall.
Also, the force of gravity on the book is not high enough to cause motion of the book to slide downs.
Frictional force is a force that opposes motion.
- For the book to slide down, it must overcome the force of friction acting on it opposite to the direction of gravity.
- According to newton's first law 'a body will remain in its state of rest or uniform motion unless acted upon by an external force'.
- Assuming the external force is gravitational force, clearly we see that the force is less than the frictional exerted on the book by pinning it to the wall.
- This frictional force is a static friction that is on a body at rest, it must be overcome by a larger force before motion takes place.
Fr > fg
Fr is the frictional force
fg is the gravitational force
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Answer:

Explanation:
We are given that


We have to find the new potential difference of the capacitor.
When the capacitor is disconnected then the charge stored in capacitor is constant.
When we introduce material of dielectric constant k between the plates of capacitor then the capacitance of capacitor increases k times.




Using the formula


Hence, the new potential difference 
Answer:
Explanation:
The current from the battery always flows from the positive terminal of the battery to the negative terminal of the battery.
If we connect a red coloured wire to the positive terminal of the battery and black coloured wire to the negative terminal of the battery, and then reverses the wire to their respective terminals, then there is no change in the direction of flow of current. It does not matter that which wire is connected to the particular terminal. The current always flow from positive to negative terminal of the battery outside the battery.
That marking means that when the expected voltage is connected
between the two contacts of the bulb, it will dissipate 100 joules of
energy every second, in the form of heat and light.