Answer:
0.5 kg
Explanation:
The momentum of an object is defined as
p = mv
where
m is the mass
v is the velocity
In this problem we have,
v = 15 m/s is the velocity of the stone
p = 7.5 kg m/s is the momentum
Solving for m, we can find the mass of the stone:

The two-second rule.
It is a common guideline to follow while driving.
It means that any given driver should be AT LEAST two seconds behind any vehicle that is driving in front of his vehicle. It might apply for any kind of vehicle.
Answer:
use the formula for option B ( d/t = s )
and
look at the graph representation to explain