EK Physics question - can someone explain this?

[dedicate]

The answer explanation in the back of the book really didn't help me at all. I'm really confused as to why the answer is what it is.

The correct answer is D, btw.

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[Jessica Stone]

The answer explanation in the back of the book really didn't help me at all. I'm really confused as to why the answer is what it is.

The correct answer is D, btw.

I don't see the complete question prompt, but I'm guessing that the force on the block is greater than the frictional force (F > uF), therefore, the block with have an acceleration (F = ma) and if it's accelerating its velocity will be increasing with time.

Think of it this way, if the force causing the block is equal to the frictional force, the block will be at equlibrium and it will have a constant velocity (if it's in motion, its velocity will be constant with time, if it's motionless, then it will remain motionless, it's velocity won't change).

If the force on the block exceeds the frictional velocity, then the block is acted upon by a force greater than that of the frictional force opposing the block. And according to Mr. Newton, anything that is acted upon by a force will have a constant acceleration (a = F/m), therefore, the velocity will increase with time.

 

[FuSoYa]

Just to add to what Jessica Stone has already said. On a velocity (or speed in this case) vs time graph the slope at any point is equal to the instantaneous acceleration. Since the force is constant, the acceleration is constant, so the slope of the V/T graph is a straight line.

 

[dedicate]

Whoops, forgot the passage lol... Ill try to get a pic up but for now I'll try to describe.

It is a block on a table. The block is connected to another block hanging straight down from a pulley.

 

[Anotherface]

The answer explanation in the back of the book really didn't help me at all. I'm really confused as to why the answer is what it is.

The correct answer is D, btw.

Since the answer is D I can tell you that there were no non-conservative forces acting on the block. Based on that information you know that it is D because the acceleration of the block is constant (i.e. the velocity is increasing linearly and the slope of the line is a constant).

 

[dedicate]

Just to add to what Jessica Stone has already said. On a velocity (or speed in this case) vs time graph the slope at any point is equal to the instantaneous acceleration. Since the force is constant, the acceleration is constant, so the slope of the V/T graph is a straight line.

Wow that really helps, never looked at it this way...

 

[rocketbooster]

use the equation v=v0 + at to find the relationship. v and t have a linear, directly proportional relationship.

if it was a velocity vs. displacement graph, you would get a graph of v=(d)^1/2. use the v^2=v0^2 + 2ad relationship for that.

this is all assuming no friction.

 

[littlejuan]

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