Answer:
Because of the presence of air resistance
Explanation:
When an object is in free fall, ideally there is only one force acting on it:
- The force of gravity, W = mg, that pushes the object downward (m= mass of the object, g = acceleration of gravity)
However, this is true only in absence of air (so, in a vacuum). When air is present, it exerts a frictional force on the object (called air resistance) with upward direction (opposite to the motion of free fall) and whose magnitude is proportional to the speed of the object.
Therefore, it turns out that as the object falls, its speed increases, and therefore the air resistance acting against it increases too; as a result, the at some point the air resistance becomes equal (in magnitude) to the force of gravity: when this happens, the net acceleration of the object becomes zero, and so the speed of the object does not increase anymore. This speed reached by the object is called terminal velocity.
The dry cleaning process uses chemicals to clean the clothes. It’s “dry” because it doesn't use water, as in normal wet laundering. Most laundries use chemicals to remove grease and stains from clothing.
Answer:
Quantity with direction and magnitude
Displacement
Explanation:
The work done is the same as the amount of energy increase. The formula for kinetic energy is 122
1
2
m
v
2
.
The initial KE of the car is 12(1000)×202=200,000
1
2
(
1000
)
×
20
2
=
200
,
000
joules.
The final KE of the car is 12(1000)×302=450,000
1
2
(
1000
)
×
30
2
=
450
,
000
joules.
The difference between these is the amount of work done: 450,000−200,000=250,000
450
,
000
−
200
,
000
=
250
,
000
joules.
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20
3
1. 450 J
2. ???
3. 1500 J
4. 800 kJ of work performed by the air conditioner
5. 2.4
6. 0 kJ
