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2 answers:
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Answer:
The focal length of the lens should be -51.5 cm (a concave lens).
Explanation:
The purpose of the lens is to make objects at 48.5 cm appear at the healthy near point. The healthy near point is 25.0 cm.
We use the lens formula
where <em>f</em> = focal length, <em>u</em> = object distance and <em>v</em> = image distance.
In this case, <em>u</em> = 48.5 cm and <em>v</em> = -25.0 cm.
<em>v</em> is negative because the image is virtual an not real. (Here, we are using the real-is-positive sign convention)
The negative sign indicates the lens is concave.
The object has a positive acceleration
Explanation:
The graph in the question is missing; find it in attachment.
The acceleration of an object is defined as the rate of change in velocity of the object:
where
is the change in velocity
is the change in time
We can verify that in a velocity-time graph, the acceleration corresponds to the slope of the graph. In fact, the slope is given by:
where
is the change in the y-variable, so it is the change in velocity,
is the change in the x-variable, so it is the change in time,
Which means that the slope is equal to the acceleration:
In this problem, the slope of the curve shown in the velocity-time graph in the figure is positive: therefore, this means that the object has a positive acceleration.
Learn more about acceleration:
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