Physics 4 Marks Questions

Yes, because tall buildings have their CM much above the ground. It increases moment of inertia of the Earth. As the Earth’s rotation does not involve torque, its angular momentum is constant. Thus, an increase in MI leads to lower angular velocity of the Earth about its axis of rotation. This means length of night and day will increase. However, the increase is very small. 

No, we cannot see the other face of the Moon from the Earth.
Yes, a person on the Moon can see all the faces of the Earth.
Explanation:
Angular velocity of the Moon about its own axis of rotation is same as its angular velocity of revolution about the Earth. This means that its rotation time period equals its revolution time period. So, we can see only one face of the Moon from the Earth.
However, angular velocity of the Earth about its axis is not same as the angular velocity of Moon about the Earth. So, all the faces of the Earth is visible from the Moon.

The ladder is more likely to slide when the man stands near the top. This is because when the man stands near the top, it creates more torque compared to the torque caused by the weight of man near the bottom.

When the man stands near the bottom, the Centre of Gravity of the ladder is shifted to C' from C. Now, the couple due to forces (m + M)g and N makes the ladder fall. We see that due to its shift from C to C', the moment arm of the couple decreases from r to r'; hence,

When the man stands near the top of the ladder, the Centre of Mass shifts from C to C'. This increases the moment arm of the couple and from r to r'. Increase in moment arm increases the couple and, thus, the ladder easily falls.

 

When the man tries to touch his toe, he exerts force along the hand downwards. This force produces amoment along the Centre of Mass CM of the man as shown in the figure. This moment makes him rotateand, thus, he falls down after losing the balance.