Motion of a block on a steep surface

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Homework Help Overview

The problem involves analyzing the motion of a block on a steep surface, specifically calculating the ratio of times taken to reach the highest point and to descend back down, considering an initial velocity and frictional forces.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the use of free body diagrams and the relationship between distance, time, and acceleration. There is an exploration of how to derive an equation that incorporates time for both ascent and descent.

Discussion Status

Some participants have provided hints regarding the relationship between time and acceleration, suggesting that the time taken to ascend and descend can be related without needing to calculate initial velocities directly. However, there is still uncertainty and confusion about applying these concepts effectively.

Contextual Notes

Participants are working within the constraints of a homework problem, which may limit the information available for deriving solutions. The discussion includes questioning the assumptions made about motion and the effects of friction.

diredragon
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Homework Statement


The block was given an initial velocity up the surface with an angle of 45 degrees to the ground. Calculate the ##\frac{t_1}{t_2}## with ##t_1## being the time it took to get to the highest point up the hill and ##t_2## the time it took to get down. In both cases the frictional force with coefficient m= 0.2 was acting on it.
2. Homework Equations
3. The Attempt at a Solution
My tried solution is uploaded below in form of a picture.
I have made free body diagrams but am stuck at getting the equation that involves time so that i can divide the two times. Any hints?
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diredragon said:
I have made free body diagrams but am stuck at getting the equation that involves time so that i can divide the two times. Any hints?

Think generally: if a body moves a distance ##d## how does the time depend on the acceleration?
 
PeroK said:
Think generally: if a body moves a distance ##d## how does the time depend on the acceleration?

##d=v_ot + \frac{1}{2}at^2##
Im still kinda stuck...
 
diredragon said:
##d=v_ot + \frac{1}{2}at^2##
Im still kinda stuck...

The body goes the same distance up the slope as it does down the slope. Down the slope is easy, as ##v_o = 0##.

You can use a trick for motion up the slope: the time taken to move a distance ##d## from an initial velocity to rest at deceleration ##a## is the same as the time to move a distance ##d## from rest at acceleration ##a##. This avoids needing to calculating ##v_0##.

To see this, think about distance as the area under a velocity/time graph.
 
PeroK said:
The body goes the same distance up the slope as it does down the slope. Down the slope is easy, as ##v_o = 0##.

You can use a trick for motion up the slope: the time taken to move a distance ##d## from an initial velocity to rest at deceleration ##a## is the same as the time to move a distance ##d## from rest at acceleration ##a##. This avoids needing to calculating ##v_0##.

To see this, think about distance as the area under a velocity/time graph.

I don't understand the trick, so in the new equation for the motion up the slope i would not have ##v_o## but would have some new ##a## while d stays the same right? How would i make that work?
 
Last edited:

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