<u>Note that</u>:
The gravitational potential energy = 
where m: is the mass, g: the acceleration due to the gravity and h is the height from the earth surface
Then, we can increase the gravitational potential energy by increasing the mass or the height from the earth surface
<u>In our question</u>, we can increase the gravitational potential energy by
<u>A) Strap a boulder to the car so that it wights more.</u>
The combined momentum is 4000 kg m/s south
Explanation:
The total combined momentum of the two cars is given by the vector addition of the momenta of the two cars.
For this problem, we choose north as positive direction and south as negative direction.
The momentum of the first car travelling north is given by:

where
is the mass of the car
is its velocity
Substituting,

The momentum of the second car travelling south is given by:

where
is the mass of the car
is its velocity (negative because the car travels south)
Substituting,

And therefore, the combined momentum is

where the negative sign means the direction of the total momentum is south.
Learn more about momentum:
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Answer:
An active pendulum has the most kinetic energy at the lowest point of its swing when the weight is moving fastest.
Explanation:
SO YOU HAVE THE LEAST KINETIC ENERGY AT THE HIGHEST POINT OF THE SWING WHEN IT'S NOT ACTIVE
a) It is absolute, so it does not change.
b) Inertial ones.
c) Inside the train the time will slow down relatively to the outside clock. So if one travel at nearly the speed if light for 2 hours on his clock, for outdoor observers it will look like 3 hours.