Answer:
(a). The 2.0 g metal cube move fast than the 4 g metal cube.
(b). The time taken is 10.19 sec.
Step-by-step explanation:
Given that,
Mass of metal cube = 2.0 g
Mass of second metal cube = 4.0 g
Coefficient of static friction = 0.65
Charging rate = 7.0 nC/s
Distance = 6.0 cm
(a). We need to calculate the frictional force for 2.0 g metal cube
Using formula of frictional force

Put the value into the formula


The frictional force for 4.0 g metal cube


The motion of the cube is less when the friction is more.
The 2.0 g metal cube is having less frictional force.
Therefore, the 2.0 g metal cube move fast than the 4 g metal cube.
(b). We need to calculate the time
Firstly we need to calculate the charge
Using electrostatic force and frictional force


Put the value into the formula




The time taken after charging beings is

Put the value into the formula


Hence, (a). The 2.0 g metal cube move fast than the 4 g metal cube.
(b). The time taken is 10.19 sec.