2. A 10 kg ball is rolled down a rail from a height of 20 m. What is the velocity at the bottom of the rail? Ignore friction.

19.8m/s

Explanation:

Given parameters:

Mass of the ball  = 10kg

Height of the rail  = 20m

Unknown:

Velocity at the bottom of the rail  = ?

Solution:

The velocity at the bottom of the rail is its final velocity.

Using the appropriate motion equation, we can find this parameter;

   V²   = U²  + 2gH

V is the final velocity

U is the initial velocity

g is the acceleration due to gravity

H is the height

  the ball was rolled from rest, U  = 0

  V²  = O²  + 2 x 9.8 x 20

 V  = 19.8m/s

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.