As a car is driven south in a straight line with decreasing speed, fhe acceleration of the car must be1) directed northward2) constant, but not zero3) directed southward4) zero

The answer is directed northward. The acceleration will be negative, since the car is decelerating. Thus the power that is slowing it down must be performing in the opposite direction to that which the car is traveling. Or in other words, when speed is lessening, acceleration is in the opposed direction to velocity. The change is CONTRASTING the velocity and so it slows it down. 

The correct option is 1) directed northward.

As a car is driven south in a straight line with decreasing speed, the acceleration of the car must be in opposite direction because car is decelerating. Therefore acceleration is negative and in the northward direction. Thus the power that is slowing it down must be performing in the opposite direction to that which the car is traveling.

Therefore the correct answer is option 1) directed northward.

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Wind or electric energy force force of friction

Wavelength divides in half and speed stays the same.