A gasoline engine receives 200 J of energy from combustion and loses 150 J as heat to the exhaust. What is its efficiency? 75% 2
2 answers:
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Answer: 585 J
Explanation:
We can calculate the work done during segment A by using the work-energy theorem, which states that the work done is equal to the gain in kinetic energy of the object:
where Kf is the final kinetic energy and Ki the initial kinetic energy. The initial kinetic energy is zero (because the initial velocity is 0), while the final kinetic energy is
The mass is m=1.3 kg, while the final velocity is v=30 m/s, so the work done is:
a) 50.8 mm
b) The whole image (1:1)
c) It seems reasonable
Explanation:
a)
To project the image on the film, the distance of the film from the lens must be equal to the distance of the image from the lens. This can be found by using the lens equation:
where
f is the focal length of the lens
p is the distance of the object from the lens
q is the distance of the image from the lens
In this problem:
f = 50.0 mm = 0.050 m is the focal length (positive for a convex lens)
p = 3.00 m is the distance of the person from the lens
Therefore, we can find q:
b)
Here we need to find the height of the image first.
This can be done by using the magnification equation:
where:
y' is the height of the image
y = 1.75 m is the height of the real person
q = 50.8 mm = 0.0508 m is the distance of the image from the lens
p = 3.00 m is the distance of the person from the lens
Solving for y', we find:
(the negative sign means the image is inverted)
Therefore, the size of the image (29.6 mm) is smaller than the size of the film (36.0 mm), so the whole image can fit into the film.
c)
This seems reasonable: in fact, with a 50.0 mm focal length, if we try to take the picture of a person at a distance of 3.00 m, we are able to capture the whole image of the person in the photo.