How does the direction of the change in velocity compared to the direction of the acceleration?
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Technically, you can simply point out that "acceleration" MEANS
"change in velocity", so of course they have the SAME direction.
Think of it like a car. When you are slowing down to stop at a light, your velocity is still going forwards, but your acceleration is negative because it is decreasing the velocity. A negative acceleration is another way of saying that the acceleration is going in the opposite direction of the frame of reference.
If the car is speeding up, the velocity is forward, and the acceleration is in the same direction because the change of velocity is positive.
Hope this helped! :D
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Light waves can also travel through space.
Sound waves, being longitudinal, are slower than light waves, and do not travel through space.
(b) 1
(c) 2
(d) 4
(e) 8
(f) None of them
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Answer:
(c) 2
Explanation:
Heat transfer across the walls due to conduction is given by:
where,
q = heat transfer rate
K = thermal conductivity
A = Area
ΔT = change in temperature
L = thickness
For wall A:
For wall B:
Because the change of temperature and area of walls are the same. Dividing both terms:
using values given in the question:
Therefore, the correct answer is:
(c) 2
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Acceleration = (change in speed) / (time for the change)
Acceleration = (990 m/s) / (35 sec) = 28.29 m/s²
Force = (mass) x (acceleration)
Force = (250,000 kg) x (28.29 m/s²) = 7.07 million Newtons
about 1.59 million pounds .
===========================================
There you have the Physics and the Math.
Does any of this resemble the real world ?
No. The question is completely bogus.
-- Take-off speed can't be 990 m/s.
That would be about 2,200 mph, almost 3 times the speed of sound.
-- The take-off run can't accelerate at 28.3 m/s² .
That would be almost 3 G's. If it didn't rip the wings off of the 747,
it would surely guarantee early use of most of the passengers' barf bags.
-- The Saturn V first-stage booster that sent Apollo to the moon
had a thrust of 7.5 million pounds. I'm pretty sure that was more
than 4.7 Boeing 747's.
================================
Ah hah ! I've just been handed a bulletin, or as they say nowadays,
there is breaking news !
I see that the take-off speed has been revised downward to 90 m/s.
That's right at 200 mph which seems reasonable to me, so let's go
back and do the whole thing again:
Acceleration = (change in speed) / (time for the change)
Acceleration = (90 m/s) / (35 sec) = 2.57 m/s² (about 0.26 G)
Force = (mass) x (acceleration)
Force = (250,000 kg) x (2.57 m/s²) = 643 thousand Newtons
about 144 thousand pounds.
about 1.9% of a Saturn V booster.
I like that a lot better.