Hello
This is a problem of accelerated motion, where the acceleration involved is the gravitational acceleration:

, and where the negative sign means it points downwards, against the direction of the motion.
Therefore, we can use the following formula to solve the problem:

where

is the initial vertical velocity of the athlete,

is the vertical velocity of the athlete at the maximum height (and

at maximum height of an accelerated motion) and S is the distance covered between the initial and final moment (i.e., it is the maximum height). Re-arranging the equation, we get
Answer:
1 km
Explanation:
Bob travels at one km/h and it takes him one hour to get there.
Answer:
D. 21 ml
Explanation:
Since, the cylinder is marked and graduated in the intervals if 1 ml. Therefore, the values between two consecutive ml, such as between 30 ml and 31 ml can not be determined. Because, we do not have any scale in between the ml. So, the least count of this instrument is 1 ml. This graduated cylinder can give the answers to zero decimal places, accurately. And it can not determine any decimal value due to its graduating or the marking limitation. So, all the options given, contain a decimal value, except for the option D. In option D there is no decimal value, hence it is a correct answer.
D. <u>21 ml</u>