You are trying to slide a refrigerator across a horizontal floor. The mass of the refrigerator is 199 kg, and you need to exert a force of 343 N to make it just begin to move.
(a) What is the coefficient of static friction between the floor and the refrigerator?
F=(mu)m*g
343\1950.2= mu
mu=.17 BUT ITS WRONG!
WHAT AM I DOING?
(b) After it starts moving, the refrigerator reaches a speed of 1.9 m/s after 4.5 s. What is the coefficient of kinetic friction between the refrigerator and the floor?
v = u + at
u =0
1.9 = 4.5 x a
a = 0.422 m/s^2
AND THATS WRONG???????????????????
I get .1758, to three significant digits. .176
On the second: find a
a= (1.9-0)/4.5 m/s^2=.42 m/s^2
Now, netforce= friction+ma
friction=netforce-ma
mu*mg=343N-199*.422
solve for mu.
To determine the coefficient of static friction between the floor and the refrigerator, you correctly used the equation:
F = μ*m*g,
where F is the force needed to make the refrigerator just begin to move, μ is the coefficient of static friction, m is the mass of the refrigerator, and g is the acceleration due to gravity.
You calculated:
F = 343 N,
m = 199 kg,
g = 9.8 m/s^2.
So the equation becomes:
343 N = μ * 199 kg * 9.8 m/s^2.
Now, let's solve for μ:
μ = 343 N / (199 kg * 9.8 m/s^2) ≈ 0.175.
The coefficient of static friction between the floor and the refrigerator is approximately 0.175.
For part (b), it seems you are trying to use the wrong equation. To determine the coefficient of kinetic friction between the refrigerator and the floor, you need to use the equation that relates the acceleration, initial velocity, time, and final velocity of an object:
v = u + at,
where v is the final velocity, u is the initial velocity, a is the acceleration, and t is the time.
From the problem statement, we are given:
u = 0 m/s (since the refrigerator starts from rest),
v = 1.9 m/s,
t = 4.5 s.
Rearranging the equation, we have:
a = (v - u) / t,
a = (1.9 m/s - 0 m/s) / 4.5 s,
a ≈ 0.422 m/s^2.
However, this value for acceleration is not directly relevant to finding the coefficient of kinetic friction. To calculate the coefficient of kinetic friction, we need the force of kinetic friction, which can be found using the equation:
F = μ_k * m * g,
where F is the force of kinetic friction, μ_k is the coefficient of kinetic friction, m is the mass of the refrigerator, and g is the acceleration due to gravity.
Unfortunately, without additional information, we cannot determine the coefficient of kinetic friction or find the force of kinetic friction in this scenario.