# Answer to Question #4808 in Mechanics | Relativity for rita

Question #4808

an accererlating force of 500N changes an object from 40 m/s to 60 m/s in a distance of 100m. the mass is 25 kg determine the force of friction acting opposite this force.

Expert's answer

Let's mark the fricting force by F. Using the second Newton's law we obtain:

500-F = 25a (1)

The average speed of an object is

(60+40)/2 = 50 m/s.

So, moving time T:

T = 100/50 = 2 s.

Let's find the acceleration of an object:

a = (60-40)/T = 20/2 = 10 m/s^2.

From (1) we obtain:

F = 500-25a = 500-25*10 = 250 N.

So, the friction force has value 250N.

500-F = 25a (1)

The average speed of an object is

(60+40)/2 = 50 m/s.

So, moving time T:

T = 100/50 = 2 s.

Let's find the acceleration of an object:

a = (60-40)/T = 20/2 = 10 m/s^2.

From (1) we obtain:

F = 500-25a = 500-25*10 = 250 N.

So, the friction force has value 250N.

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