Question

Плот , на котором пребывает мальчик массой 65кг.плывет по речке со скоростью 0,5м/с,Определите скорость движения плота сразу после того ,как мальчик спрыгнул с него со скоростью 1м/с относительно берега в направлении движения плота.Масса плота 120кг.

Answer 1

М=120кг

m=65кг

V=0,5м/c

v=1м/с

V1-?

(m+M)*V=m*v +M*V1

M*V1=(m+M)*V -m*v

V1=(m+M)*V -m*v  /M

V1=(65+120)*0,5 -65*1 /120=1м/с

Answer 2

Calculation of the Speed of the Raft

To determine the speed of the raft immediately after the boy jumps off, we need to consider the conservation of momentum. The initial momentum of the system (raft + boy) is equal to the final momentum of the system after the boy jumps off.

The initial momentum of the system is given by the product of the mass of the boy and the velocity of the raft: Initial momentum = (mass of the boy) * (velocity of the raft)

The final momentum of the system is given by the sum of the momentum of the raft and the momentum of the boy after he jumps off: Final momentum = (mass of the raft) * (velocity of the raft after the boy jumps off) + (mass of the boy) * (velocity of the boy after he jumps off)

Since momentum is conserved, we can equate the initial momentum to the final momentum and solve for the velocity of the raft after the boy jumps off.

Let's plug in the given values: - Mass of the boy = 65 kg - Velocity of the raft = 0.5 m/s - Velocity of the boy after he jumps off = 1 m/s - Mass of the raft = 120 kg

Initial momentum = Final momentum (mass of the boy) * (velocity of the raft) = (mass of the raft) * (velocity of the raft after the boy jumps off) + (mass of the boy) * (velocity of the boy after he jumps off)

Substituting the given values: (65 kg) * (0.5 m/s) = (120 kg) * (velocity of the raft after the boy jumps off) + (65 kg) * (1 m/s)

Now we can solve for the velocity of the raft after the boy jumps off.

Calculating the equation: (65 kg) * (0.5 m/s) = (120 kg) * (velocity of the raft after the boy jumps off) + (65 kg) * (1 m/s) 32.5 kg·m/s = (120 kg) * (velocity of the raft after the boy jumps off) + 65 kg·m/s

Simplifying the equation: 32.5 kg·m/s - 65 kg·m/s = (120 kg) * (velocity of the raft after the boy jumps off) -32.5 kg·m/s = (120 kg) * (velocity of the raft after the boy jumps off)

Dividing both sides by 120 kg: -32.5 kg·m/s / 120 kg = velocity of the raft after the boy jumps off

Calculating the value: velocity of the raft after the boy jumps off = -0.2708 m/s

Therefore, the speed of the raft immediately after the boy jumps off, in the direction of the raft's motion, is approximately -0.2708 m/s. The negative sign indicates that the raft is moving in the opposite direction to its initial motion.

Please note that the negative sign indicates the direction of the velocity, not the speed. The magnitude of the velocity is 0.2708 m/s.