(a) how much work is done when you push a crate horizontally with 100 n across a 10-m factory floor?
(b) if the force of friction in the crate is a steady 70 n, show that the ke gained by the crate is 300 j.
(c) show that 700j is turned into heat.

A) 1000 joules

Explanation:

In general work is given by the equation:

(1)

A) With the displacement and the force applied, because the force and the displacement are parallel (the crate is pushed horizontally) is simply , and because the path is a straight line and the force is constant work is:

(2),

B) The work-energy theorem says that the total work on a body is equal to the change on kinetic energy:

(3)

The total work on the crate is the work done by the push and plus the work of the friction (4) , as (A) because forces are parallel to the displacement (5) and (6), the due friction always has negative sign because is opposite to the displacement, using (6), (5) and (4) on (3):

(3)

C) The energy is lost by friction, so the amount of energy turned into heat is the work the friction does:

(3)

close lines strong magnet less close weaker

thermal energy is the answer