Kinematics from AAMC 4

[DeathandTaxes]

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Consider a block attached to a hook. Where would energy for such a system come from?
How the speed of the block varies over time. I said that it increases exponentially, because speed (as I take it, should be distance/time), and if it has constant acceleration, then only an exponentially increasing distance would have a positive second derivative. The answer is that speed increases at a constant rate (because speed = velocity). Is that really the convention for defining speed?

 

[justwantanmdphd]

Hello @DeathandTaxes , I think you have the right idea. when the choice C said "block" it meant the block on the table, which is not moving because of its own PE. the KE is coming from the block on the hook (mass on the hook). The mass on the hook is pulling it down like you said. it's a matter of word choice.
for the second question: if speed increases exponentially, then there is an increasing acceleration. (think of the vt and at graphs: exponential vt graph gives you increasing acceleration. but "g" is constant, so you need a constantly increasing speed to give you a horizontal line in at graph to get a constant acceleration). hope that helps.

 

[el_duderino]

The block is the part sitting on the table. The mass is the part that's moving down the gravity well.

As for speed, speed increases linearly. Think about units of acceleration: meters per second squared. Meters per second.. per second. For constant acceleration, the meters per second increases by a fixed amount per unit time.