We're told to find the coefficient of friction for a mousetrap car that we've made, using values that we attained ourselves. We released the arm of the mousetrap onto a scale to find Fa → 1.0*10^2 Newtons.
This is how we found Fa:
m = 1.020kg (←mousetrap held back and hammer released onto scale, value recorded from scale)
a = 9.8m/s/s (←factoring in gravity, which affects mousetrap's "release weight" on scale)
Fa = ?
Fa = ma
= 1.020kg * 9.8m/s/s (Fg)
= 9.996 Newtons
= 10. Newtons (← rounded to correct amount of sig digs.)
Using that, we solved for acceleration :
Vi = 0.0m/s
t = 1.56s (time to complete 3m)
d = 3.0m
a = ?
d = Vi(t)+0.5a*(t^2)
a = (3m)/(0.5)(1.56^2)
a = 2.46 m/s/s
= 2.5m/s/s (← rounded to correct amount of sig digs.)
With that Ff and Fnet was solved for :
Fa = 10. Newtons
m = 0.128kg
a = 2.5m/s/s
Ff = ?
Ff was needed later so rather than doing m*a to find Fnet, we found Ff first to find Fnet:
Fnet = ma
Fa + Ff = ma
Ff = 0.128kg(2.5m/s/s)- 10. Newtons
Ff = -9.68 Newtons
= -9.7 Newtons (← rounded to correct amount of sig digs.)
And now Fnet:
Fnet = Fa-Ff
= 10. Newtons - 9.7 N
= 0.3 Newtons
At this point, everything seemed reasonable, but then we needed to solve for the coefficient of friction.
μk = Fk/Fn
The Attempt at a Solution
μk = Fk/Fn
= -9.7 Newtons / (0.128)*(9.8)
= 7.7 (← rounded to correct number if sig digs.)
The question is, does 7.7 make sense for a coefficient of friction, and does everything else look sound?. The mousetrap car we made seemed to be of low friction , except between the ground and the wheel, where we wanted to maximize friction (balloons were used).