Question

Из неподвижной лодки, масса которой 80 кг, прыгает на берег мальчик. масса мальчика 40 кг, скорость его при прыжке 2 м/с. какую скорость приобрела лодка?

Answer 1

Ну вот:
m1=80кг
m2=40кг
v2=2м/с
---------------
v1- ?
 закон сохранения импульсаm
1v1 +m2v2 =0
v1 = -m2v2/m1= -40*2/80= -1 м/с 
Ответ скорость лодки  1м/с

Answer 2

Problem Analysis

We are given a scenario where a boy jumps from a stationary boat to the shore. The mass of the boat is 80 kg, the mass of the boy is 40 kg, and the boy's jumping speed is 2 m/s. We need to calculate the speed acquired by the boat after the boy jumps.

Solution

To solve this problem, we can use the principle of conservation of momentum. According to this principle, the total momentum before the jump is equal to the total momentum after the jump.

The momentum of an object is given by the product of its mass and velocity. Therefore, the momentum of the boat before the jump is 80 kg * 0 m/s = 0 kg·m/s, since it is stationary. The momentum of the boy before the jump is 40 kg * 0 m/s = 0 kg·m/s, as he is also stationary.

After the jump, the boy acquires a velocity of 2 m/s. Let's assume the velocity acquired by the boat is v m/s. The momentum of the boy after the jump is 40 kg * 2 m/s = 80 kg·m/s, and the momentum of the boat after the jump is 80 kg * v m/s = 80v kg·m/s.

According to the principle of conservation of momentum, the total momentum before the jump is equal to the total momentum after the jump. Therefore, we can write the equation:

0 kg·m/s + 0 kg·m/s = 80 kg·m/s + 80v kg·m/s

Simplifying the equation, we get:

80v kg·m/s = -80 kg·m/s

Dividing both sides of the equation by 80 kg·m/s, we get:

v = -1 m/s

Therefore, the boat acquires a velocity of -1 m/s after the boy jumps.

Answer

The boat acquires a velocity of -1 m/s after the boy jumps.

Explanation

When the boy jumps from the stationary boat to the shore, the boat acquires an equal and opposite velocity to conserve momentum. Since the boy jumps with a velocity of 2 m/s, the boat acquires a velocity of -1 m/s. The negative sign indicates that the boat moves in the opposite direction to the boy's jump.