A72.3-kg person, running horizontally with a velocity of +2.99 m/s, jumps onto a 13.9-kg sled that is initially at rest. (a) ignoring the effects of friction during the collision, find the velocity of the sled and person as they move away. (b) the sled and person coast 30.0 m on level snow before coming to rest. what is the coefficient of kinetic friction between the sled and the snow?

(a) 2.51 m/s

(b) 0.011

Explanation:

mass of person, M = 72.3 kg

initial velocity of person, U = 2.99 m/s

mass of sled, m = 13.9 kg

initial velocity of sled, U = 0

(a) Let the velocity of person and the sled is V

By using the conservation of momentum

M x U + m x u = (M + m) x V

72.3 x 2.99 + 13.9 x 0 = (72.3 + 13.9) V

216.177 = 86.2 V

V = 2.51 m/s

(b) initial velocity , V = 2.51 m/ s

Final velocity, V' = 0

distance, s = 30 m

Let μ be the coefficient of friction.

Use third equation of motion

0 = 2.51 x 2.51 - 2 x μ x 9.8 x 30

μ = 0.011

it is given that trillions of microbes make up to 1% to 3% of the body mass.

let's take average of this percentage: 2%

consider the average mass of the human body as 70 kg.

then, trillions of microbes would have mass  

therefore, 100 trillion micro-organisms would weigh:

this is an approximate value and could change depending on the mass of the human body and percentage of the microbes present in it.

average mass per microorganism =