A disc with a mass of 1 kg moves horizontally to the right with a speed of 7 m/s on a table with negligible friction when it col
lides with a second disc with a mass of 9 kg. The second disc is moving horizontally to the right with a speed of 1 m/s at the moment of impact. The two discs stick together upon impact. What is the speed of the composite body immediately after the collision? (round your answer to the nearest tenth)
1 answer:
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Answer:
<em>Correct choice: b 4H</em>
Explanation:
<u>Conservation of the mechanical energy</u>
The mechanical energy is the sum of the gravitational potential energy GPE (U) and the kinetic energy KE (K):
E = U + K
The GPE is calculated as:
U = mgh
And the kinetic energy is:
Where:
m = mass of the object
g = gravitational acceleration
h = height of the object
v = speed at which the object moves
When the snowball is dropped from a height H, it has zero speed and therefore zero kinetic energy, thus the mechanical energy is:
When the snowball reaches the ground, the height is zero and the GPE is also zero, thus the mechanical energy is:
Since the energy is conserved, U1=U2
For the speed to be double, we need to drop the snowball from a height H', and:
Operating:
Dividing [2] by [1]
Simplifying:
Thus:
H' = 4H
Correct choice: b 4H