A cart of mass m moving right at speed v with respect to the track collides with a cart of mass 0.7m moving left.
What is the initial speed of the second cart if after the collision the carts stick together and stop?
Express your answer in terms of some or all of the variables m and v.

10/7 * V.

Explanation:

Momentum = mass * velocity

Given:

Mass of cart 1 = M1

Mass of cart 2 = M2

= 0.7M1

Initial velocity of cart 1 = Vi1

= V

Initial velocity of cart 2 = Vi2

Final velocity = V

= 0

Initial momentum of cart 1 + initial momentum of cart 2 = total mass of both cart * velocity

M1 * Vi1 + M2 * Vi2 = (M1 + M2) * V

= M * V - (0.7M * Vi2) = (M + 0.7M) * 0

= MV - 0.7M * Vi2 = 0

Vi2 = 10/7 * V.

the average speed is 24.57 km/hr