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Chartwig1908
20.04.2020 •
Physics
A small wooden block with mass 0.800 kg is suspended from the lower end of a light cord that is 1.44 m long. The block is initially at rest. A bullet with mass 0.0134 kg is fired at the block with a horizontal velocity v0. The bullet strikes the block and becomes embedded in it. After the collision the combined object swings on the end of the cord. When the block has risen a vertical height of 0.800 m , the tension in the cord is 4.76 N .
What was the initial speed v0 of the bullet?
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Ответ:
v₀ = 240 m / s
Explanation:
This problem must be solved in two parts, first we must use the conservation of the moment, then the conservation of energy.
Let's start by applying moment conservation, to the system formed by the block and bullet, in this case the forces during the crash are internal and the moment is conserved
Instant starts. Before the crash
p₀ = m v₀
Final moment. Right after the crash
The moment is preserved
Po =p_{f}
M v₀ = (m + M) v
v = m / (m + M) v₀ (1)
This is the speed with which the bullet block system comes out, now we can use energy conservation
Starting point. Right after the crash
Em₀ = K = ½ (m + M) v²
Final point. Highest point of the path
Em₀ = Em_{f}
½ (m + M) v² = (m + M) g y
v = √2 g y (2)
We substitute 1 in 2
m / (m + M) v₀ = √ 2gy
v₀ = (m + M) / m √ 2gy
Let's calculate
v₀ = (0.0134 +0.800) /0.0134 √ (2 9.8 0.8)
v₀ = 240 m / s
Ответ:
B easy bruising
Explanation:
A bruise is medically termed a contusion. ... Easy bruising can occur when the blood vessels are weakened by diseases (such as scurvy), medications (such as aspirin, prednisone, and prednisolone), and aging. Easy bruising can also occur because of absent or deficient blood-clotting elements.