Search 73,878 tutors
0 0

# An object is falling at a rate that is 60% of the acceleration of gravity....

An object is falling at a rate that is 60% of the acceleration of gravity
therefore it is pressing down on anything below it with:

A> 100% of its mass

B> 60% of its mass

C> 140% of its mass

D> 40% of its mass

If N is the force pressing down, then -N is the exterior force pressing it up.
Applying Newton's second law in vertical direction, with downward direction as positive,
mg - N = ma
N = mg-ma = mg - 0.6mg = 0.4 mg

In the reference frame of an object there is an upward force, acting against the gravity and equal to 0.6 mg, where m is the mass of an object.

Therefore, the object is pushing on anything below it with mg-0.6 mg=0.4 mg force, which is equivalent to the 40% of its normal weight.

Thanks this helps!
This is simply a poorly worded question. It's the kind of question that gives physics a bad name. If there is an upward force pulling up on the object (parachute as James said or a small rocket etc) then there will be no force on an object below. Shan should ask for a clarification from the teacher.
Unfortunately, I am not sure that some of the answers given here are correct! The confusion may be arising with the wording of the question If you look at the answer choices they are all expressed in terms of a percent of the mass of the object, not a percent of the weight of the object.

A distinction has to be made between the mass of the object, given by m, and its weight, which is mg. The weight of an object can be different under different conditions because this depends on g, however, the mass will remain the same unless it is being converted to energy (E = mc^2).

Therefore, in terms of the mass, I think the correct answer is A, i.e. 100% of its mass! Regardless of the upward forces experienced by an object, it will always press down on something below it with 100% of its mass.

An object that is falling is not pressing down on anything. What you mean is: an object in a reference frame that is accelerating down at 60% of the acceleration of gravity (like an elevator) will experience which upward force? This is called the object's apparent weight and it is indeed 40% of its real weight. The object's mass is not affected by this.
Although I do agree with the two answers given, I wanted to give you some food for thought.

Technically the Earth is below the person falling. Even though you are not free falling, you are still pulling up on the Earth by your weight (mg).

Additionally, you are assuming there are only 2 forces acting on the falling person. That is, there is only the force due to gravity and an opposing force below the falling person (typically air resistance). However there could be more forces present and being applied by an object not necessarily below the person falling (ie a parachute).

Just some things to think about.