Two commuter rail cars, one from shah alam and the other from kuala lumpur approach each other on parallel tracks. each has a speed of 100km/h with respect to the earth. if they are initially 10km apart, how long will it be before they pass each other?

They meet after the time t from the departure

During this time, one goes through the distance

S1 = V1 * t

and the second goes through the distance

S2 = V2 * t

The sum of the two distances gives us total distance

S1 + S2 = S

Replace S1 and S2 in this last equation

V1 * + V2 * t = S

t (V1 + V2) = S where we take out the time they meet

t = S / (V1 + V2)

V1 = V2

t = 10 / 2V1 = 10/200 = 0.05 hours

D) the force of gravity from the rock on the Earth

Explanation:

When a rock  is under free fall , it is acted upon gravitational force by the earth . This is action force by the earth on the rock  . According to newton's third law , there will be a reaction force also .  Force is creating due to mutual attraction between earth and rock so rock will also exert gravitational force on the earth . Hence, that force will be reaction force .

Force due to rock on the earth will be reaction force , according to newton's third law.