The force exerted by gravity on a 25 lb object lifted to a height of 6.0ft above the ground is _____ N. ( Given work done = 2.0 × 10² J)

Question

Quizplus · Accepted Answer

The work done is equal to the potential energy gained by the object. 
Work done(W) = potential energy gained(mgh)
where m is the mass of the object, g is the acceleration due to gravity and h is the height to which the object is lifted.
Here, the mass of the object is not given but its weight is given as 25 lb. We know that the weight of an object is the force exerted on it by gravity. 
Weight = force = mass x acceleration due to gravity
or m = weight/acceleration due to gravity = 25/32.2 lb
Now, we can calculate the potential energy gained as
potential energy gained = mgh = (25/32.2) x 32.2 x 6 = 25 x 6 = 150 lb-ft = 150 x 1.3558 J 
= 2.0327 x 10^2 J (approx)
The force exerted by gravity is equal to the weight of the object, which is 25 lb or 111.2 N (approx).
The closest answer choice to this value is A) 1.1 × 10^2 J.

The Force Exerted by Gravity on a 25 Lb Object