Aweight lifter struggles but manages to keep a heavy barbell abovehis head. occasionally he slips and the barbell starts to fall downward, but he always recovers. in each case, compare the force exerted by the weight lifter on the barbell to that exerted by the barbell on the weight lifter.

a)- with the barbell at rest.
b)- with the barbel moving upward.
c)- with the barbel moving downward.

Explanation:

(A)

-With the barbell at rest- Both forces are equal

When the barbell is at rest then in this condition both forces are equal. The force exerted by the weight lifter on the barbell is equal to the force exerted by the barbell on the weight lifter.

(B)

-With the barbell moving upward- Forces are equal

When the barbell is moved upward by the weight lifter then the force exerted on the barbell by the weight lifter is greater than the gravitational force exerted on the barbell.

(C)

-With the barbell moving downward-Forces are equal

When the barbell is moved downward by the weight lifter then the force exerted on the barbell due to gravity is greater than the force exerted by the weight lifter on the barbell.

5 w for 1hr = 5x60x60 joules=300x60=3000x6=18,000j as total energy conversion. efficiency of bulb needed for radiant to thermal within 18000