Answer: 
Explanation:
Given
Length of plank is 1.6 m
Force 
is applied on the left side of plank
Force 
is applied 43 cm from the left end O.
Mass of the plank is 
for equilibrium
Net torque must be zero. Taking torque about left side of the plank
Net vertical force must be zero on the plank
The accurate description of the process of erosion is when <span>moving bits of rock and soil across the earth’s surface by water, wind, or glaciers. The answer is letter C.</span>
Microwaves and radio waves are employed in radio and satellite communications while infrared waves are used in remote controls and infrared features of new phones and other electrons. However, gamma rays have far too much energy and cause damage to the body. They are not used in communication.
The answer is A.
Density
is a value for mass, such as kg, divided by a value for volume, such as m3.
Density is a physical property of a substance that represents the mass of that
substance per unit volume. It is a property that can be used to describe a
substance.<span> </span><span>It has standard units of
kg/m^3 or g/mL.
So, the best answer is option C.</span>
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.
