A man weighing 60 kg, running at a speed of 18 km / h, catches up with a cart weighing 40 kg

| September 9, 2021 | education

A man weighing 60 kg, running at a speed of 18 km / h, catches up with a cart weighing 40 kg, moving at a speed of 2 m / s, and jumps on it. How fast will they keep moving?

Given:

m1 = 60 kilograms – the mass of a person;

v1 = 18 km / h = 5 m / s – human speed;

m2 = 40 kilograms – the mass of the cart;

v2 = 2 m / s – trolley speed.

It is required to determine the speed of the joint movement of a person and a cart v (m / s).

Since, according to the condition of the problem, a person catches up with the cart, their speeds are directed in one direction. Then, according to the law of conservation of momentum (momentum):

m1 * v1 + m2 * v2 = (m1 + m2) * v;

v = (m1 * v1 + m2 * v2) / (m1 + m2) = (60 * 5 + 40 * 2) / (60 + 40) =

= (300 + 80) / 100 = 380/100 = 3.8 m / s.

Answer: the person and the cart will move at a speed of 3.8 m / s.



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