tbr physics translational motion

[AntonFreeman]

this is from TBR.

"according to aristotle, objects at rest tend to remain at rest. It follows that if an object is released from rest and allowed to fall vertically, the object should not fall, since its natural tendency is to remain at rest." this statement:

c.is false; galileo demonstrated that an object's natural tendency is to remain in motion.
d.is false: it is possible for an object's velocity to be zero while its velocity's rate of change is not zero.

answer is d. but i have a hard difficult time understanding why D is the better answer than C.

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[muhali3]

An object's natural tendency is to remain in motion only if it was in motion originally. C is not completely true, only the "is false" part is true.

D is true because an object's instantaneous velocity can be zero while it's acceleration is not zero. ie. a ball thrown upwards, at its maximum height, has zero velocity but still has a downwards acceleration of g.

 

[BilalL]

this is from TBR.

"according to aristotle, objects at rest tend to remain at rest. It follows that if an object is released from rest and allowed to fall vertically, the object should not fall, since its natural tendency is to remain at rest." this statement:

c.is false; galileo demonstrated that an object's natural tendency is to remain in motion.
d.is false: it is possible for an object's velocity to be zero while its velocity's rate of change is not zero.

answer is d. but i have a hard difficult time understanding why D is the better answer than C.

An object dropped from your hand can have an instantaneous velocity of zero while still be affected by gravitational acceleration. So the change of rate is not zero. You should study the vertical velocity a bit more. Velocity on the vertical vector reaches zero in a lot of projectile motion problems, yet acceleration(in this case gravity) is always affecting it. In many of these cases, since there is a horizontal velocity vector as well, overall velocity is never zero.

An object IN Motion, tends to remain in motion unless another force acts upon it. An object at rest tends to remain at rest in a similar manner. So C is false.