The hummingbird shown here must beat its wings repeatedly to hover over flowers and drink nectar. what force does the beating of the hummingbird’s wings overcome?
a) entropy
b) gravity
c) inertia
d) momentum

A) entropy 
B) gravity 
C) inertia 
D) momentum

The answer is B;

Gravity. 

Have a nice day! :)

Since the pully is a simple machine so the mechanical advantage is a 1

Year  1936,  lehman predicted that the earths 'inner core' is solid. she observed that the seismic signals during her study were bent and did not pass through instead bouncing back. later it was confirmed that the earth's inner core was solid made up of nickel-iron and had a molten outer core.