An incident ray that passes through the vertex of a concave lens

Which simple machine is not part of this compound machine? a. lever b. pulley c. inclined plane d. wheel and axle

The force acting on a beam was measured under the same operating conditions and a sample of 5 data points was collected. this process was repeated by 3 observers. the pooled standard deviations of these 3 data sets was 1.21. determine the true mean force using all pooled data (with a 95% probability). the result should look like this: true mean = mean +/- margin of error

The necleus of an atom is made up of what subatomic particles?