To solve this problem, we should recall the law of
conservation of energy. That is, the heat lost by the aluminium must be equal
to the heat gained by the cold water. This is expressed in change in enthalpies
therefore:
- ΔH aluminium = ΔH water
where ΔH = m Cp (T2 – T1)
The negative sign simply means heat is lost. Therefore we
calculate for the mass of water (m):
- 0.5 (900) (20 – 200) = m (4186) (20 – 0)
m = 0.9675 kg
Using same mass of water and initial temperature, the final
temperature T of a 1.0 kg aluminium block is:
- 1 (900) (T – 200) = 0.9675 (4186) (T – 0)
- 900 T + 180,000 = 4050 T
4950 T = 180,000
T = 36.36°C
The final temperature of the water and block is 36.36°C
Answer:
A) being influenced by equal amounts of gravity and air resistance.
Explanation:
B) slowing down because of an unbalanced force of air resistance.
False - if it was slowing down, then the velocity would go down.
D) on the ground and is not falling anymore.
False - This would be mistaken as the answer but it is not because if the person is not falling anymore the horizontal line should be at the x-axis, meaning that there is no more velocity.
C) accelerating because of an unbalanced force of gravity.
False - The line would otherwise be going up or down.
Yes. Think of block sitting on top of a bigger block. If the bottom block moves, it will drag the top block with it. Since the force of friction on the small block and its displacement are in the same direction, the "work" is positive. The static friction is a passive force, It is not a source of energy; it transmits the force placed on the bottom block. (And the "work" done by the friction on the bottom block is exactly the negative of the work done on the top block.)
Answer:
it is constant because there is not any force that oppose the horizontal motion
but the vertical velocity is not constant because there is a gravitational force that oppose the motion .
