Answer:
40 cm
Explanation:
The focus of a spherical convex mirror is the point at which the rays of an object converge in the infinite, it is also the point at which an object must be placed so that its image is formed in the infinite. The distance from the focus to the origin is called the focal length and is called f. It is related to the radius of the mirror, R, according to:

rewriting for R:
.
Kinetic energy, KE, is modeled by the formula

, where m is the mass in kg and v is the velocity in m/s.
In this scenario, mass and one-half are constant but the velocity changes.
You can see that by squaring twice the velocity, that is equal to four times the original KE. Therefore, the answer is 4k.
1850 to 1900 because the slope would be 105. It says what is the greatest fall, so the upward slope of 120 wouldn't count.