When the ruler is broughı near the inetal knob, it repels electrons in the metal. Electrons move away froni the ruler and down the metal rod. The knob now has a positive charge. The thin pieces of metal foil at the bottom of the metal rod now have a negative charge.
Answer:
126.99115 g
Explanation:
50 g at 90 cm
Stick balances at 61.3 cm
x = Distance of the third 0.6 kg mass
Meter stick hanging at 50 cm
Torque about the support point is given by (torque is conserved)

The mass of the meter stick is 126.99115 g
Answer:
Work done in both the cases will be same
Explanation:
As we know that the work done against gravity is given as

here we know that gravitational force is a conservative force and the work done against gravitational force is independent of the path
So here the work done by person to move the object between two different heights will be independent of the path they choose
So for the first person and second person will be same in both the cases because the height through which the boxes are transferred will be same in both the cases
What you need to know is that the force is
F=ma
The force is the product of mass and acceleration
this means that the acceleration is
a=F/m
a) The force is halved?
this means that f will be

now:
a=

So the accelaration will also he halved (it's the original acceleratation divided by 2)
b) The object's mass is halved?
a=

=a=

which is the original acceleration times two!! so it will double
c) The force and the object's mass are both halved?
now we have
a=

=a=

=a=

so they will cancel each other out and the acceleration will stay the same!