Find how long a marble rolls down a ramp, given distance and angle

[camelCaseD]

Homework Statement

How many seconds does it take a marble to run down a ramp with a length of 5.0 m and an angle of 6.9°?
Correct answer = 2.9 s.

Homework Equations

v = at
d = 1/2at²

The Attempt at a Solution

√2(5)/9.8≠2.9 s

 

[tiny-tim]

hi camelCaseD! welcome to pf!

where did you use the 6.9° ?

(or the fact that it rolls)

 

[camelCaseD]

I'm not sure if the angle is relevant information for solving the problem or not. But the length of the ramp and the angle its at are the only given data I have. The marble does roll down the ramp.

 

[tiny-tim]

I'm not sure if the angle is relevant information for solving the problem or not.

?? but if this 5m ramp was at 0.01°, wouldn't it take a lot longer than if it was at 90° ?

 

[camelCaseD]

?? but if this 5m ramp was at 0.01°, wouldn't it take a lot longer than if it was at 90° ?

Yes it would be slower if the angle were 0.01° than 90°.

 

[tiny-tim]

yes!

sooo … ? ​

 

[camelCaseD]

So then since the angle of the ramp is at 6.9° the time it would take the marble to roll down the ramp would take longer than if it were straight up and down.

 

[tiny-tim]

yes, but what equation are you going to use?

(and now I'm off to bed :zzz:)

 

[camelCaseD]

I'm going to use the equation d=1/2at²

 

[tiny-tim]

(just got up :zzz:)

I'm going to use the equation d=1/2at²

yeeees …

but first you need to find a (the component of acceleration down the ramp)!​

what equation will you use for that?