Help with free fall c/o physical science

Question

 

1.  in a free fall any object no matter what its mass accelerates....

 

a.  at the same rate

b.  according to the formula F/m

c.  both a and b

 

 

I agree with c

 

 

2.  when air drag and the pull of gravity on a parachutist are equal...

 

a.  the parchutist stops accelerating

b.  the accelerating is g

c.  the parachutist's speed is  0

 

 

I don't think the answer is b

 

 

Answer 1

Hello L,

 

1. There are many types of forces in physics; however, if we are talking about free fall, we are specifically talking about the force due to gravity or in other words:

 

Fg = mg,

 

where g is always a constant (same) acceleration rate of -9.8m/s^2. I believe a. is the correct answer.

 

2. For the second part, its the same problem, but now we have another force, "air drag" and this force is equal and opposite of the force due to gravity, Fg. So if we use Newton's famous equation and sum the forces in the y-direction, we get a net acceleration equal to zero! (Acceleration due to air drag is a resistive force, so it acts in the direction opposite of motion). This means that the parachuist stops accelerating and this is also known as reaching "terminal velocity." The correct answer should be a.

Answer 2

In a normal case (vacuum/physics conditions), your guess of C for number one would be right, however, that implies that the force on each object was equal or at least approximately equal.  In the case of your questions, I believe it would be more correct to simply say B as there are other forces effecting the acceleration of an object in free fall such as air resistance.

 

The example of the parachutist in your second question is a good example of this.  In this case they ask you to assume that the force from air resistance on the parachute and that of the pull of gravity are equal, so knowing that F=m/a and mass doesn't change, if the total force on the object is 0, then the acceleration must be 0 (answer A).  In this example of a free fall object, this state is known as terminal velocity (the rate at which an object falls where air resistance equals the force of gravity and thus cannot fall any faster).

 

Hope this helps,