# Homework Help: Propagation of errors addition numbers without uncertainty

1. Oct 4, 2011

### Silvestor

1. The problem statement, all variables and given/known data
I am having trouble calculating uncertainty when a number is added to a value with uncertainty.

M = 350g
a = 0.624 $\pm$ 0.001
µk = 0.07
g = 9.80 m/s2

2. Relevant equations
T = M*a + µk*M*g

3. The attempt at a solution
T = (350g)*(0.624 m/s2) + (0.07)*(350g)*(9.80m/s2)
T= 458.5 N
D$_{}t$ = M*(D$_{}a$) + ......
D$_{}t$ = (350g)*(0.001 m/s2) + ......
D$_{}t$ = 0.35 N + ....

2. Oct 4, 2011

### Staff: Mentor

If you're given that there is no uncertainty in M, g, or µk then you treat them as constants that are 100% accurate. The uncertainty in the result, then, only depends upon the uncertainty in a, as you've written. The uncertainty in the µk*M*g term is zero.

3. Oct 4, 2011

thanks