The larger mass object would have more kinetic energy. 1) its heavier 2) it covers a larger area 3) the more mass an object has, the larger the kinetic energy because of its weight.
The charge on the electron is 1.6x10^-19C. So, 10^24 of them will be a charge of 1.6x10^5C, F = q1xq2/[(4pi epsilon nought)r^2]
D = distance between the cars at the start of time = 680 km
v₁ = speed of one car
v₂ = speed of other car = v₁ - 10
t = time taken to meet = 4 h
distance traveled by one car in time "t" + distance traveled by other car in time "t" = D
v₁ t + v₂ t = D
(v₁ + v₂) t = D
inserting the values
(v₁ + v₁ - 10) (4) = 680
v₁ = 90 km/h
rate of slower car is given as
v₂ = v₁ - 10
v₂ = 90 - 10 = 80 km/h