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A child in a boat throws a 6.6kg package out horizontally with a speed of 10.2m/s. Calculate the velocity of the boat immediately after, assuming it was initially at rest. The mass of the child is 29.9kg, and that of the boat is 44.7kg. Ignore water resistance.

User Michael Blanza
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2 Answers

27 votes
27 votes

Final answer:

The velocity of the boat immediately after the package is thrown is 10.0 m/s in the opposite direction to the package.

Step-by-step explanation:

To solve this problem, we can apply the principle of conservation of momentum. The initial momentum of the system (boat + child) is zero since both are initially at rest.

The momentum of the package can be calculated using the equation:

momentum = mass × velocity

Since the package is thrown horizontally, its velocity is only in the x-direction. Therefore, the momentum of the package is (6.6 kg) × (10.2 m/s) = 67.32 kg·m/s.

According to the conservation of momentum, the final momentum of the system (boat + child + package) must also be zero.

Let's assume the velocity of the boat after the package is thrown is v.

The momentum of the boat is given by:

momentum = mass × velocity

The child's momentum is given by:

momentum = mass × velocity

The momentum of the system after the package is thrown is the sum of the momenta of the boat, child, and package.

We can express this as an equation:

(mass of boat × v) + (mass of child × 0) + (mass of package × 10.2 m/s) = 0

Since the mass of the child is 29.9 kg and the mass of the boat is 44.7 kg, the equation becomes:

(44.7 kg × v) + (29.9 kg × 0) + (6.6 kg × 10.2 m/s) = 0

Solving this equation, we find that the velocity of the boat after the package is thrown is approximately -10.0 m/s.

The negative sign indicates that the boat is moving in the opposite direction to the package.

Therefore, the velocity of the boat immediately after the package is thrown is 10.0 m/s in the opposite direction to the package.

User Scott Kilbourn
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3.1k points
11 votes
11 votes

Answer:


-0.902 \frac ms

Step-by-step explanation:

We apply conservation of momentum here. Before the toss, everything was still, so the momentum was 0. After the toss, we have the sum of the momentum of the package (1st term) and the boat+child combo (2nd term). Let's call v the velocity of the boat.


0= 6.6kg \cdot 10.2\frac ms + (29.9+44.7)kg\cdot v\\v= - (6.6 \cdot 10.2 )/(74.6) \frac ms \approx -0.902 \frac ms

The term is negative since it expresses the boat+child system is going the opposite way from where the package flew.

User Jakber
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