2 Falling Objects - Center of mass velocity?

Question

Consider two falling bodies. Their masses are 1.8 kg and 6.2 kg. At time t = 0, the two are released from rest. What is the magnitude of the velocity of their center of mass at t = 1.2 s? Ignore air resistance.

This is like another one I have found on here, but the masses in that one are the same.... help!

Answer 1

The masses don't matter, because acceleration due to gravity isn't affected by mass. Both objects will move downwards such that, at any given moment, they have the same speed, and their center of mass will also have that same speed. The acceleration is g = 9.8 m/s^2, and the velocity will be g*t = (9.8 m/s^2)*(1.2 s) = 11.76 m/s.

Answer 2

Ignoring air resistance all objects regardless of mass fall at exactly the same rate. This was confirmed on the first moon landing in 1969 when an astronaut dropped a hammer and a feather from 6 ft. on the surface of the moon. Both landed at exactly the same time. The rate of acceleration will vary with the planets mass.

Answer 3

No time to really go into it at the moment..... But Potential energy of an item 2000m above ground is measured in Joules. ( or kilojoules). Yes you do need to get the Joules out of the velocity, I suggest you have a simultaneous equation issue first with two equations expressed as -60 j m/s and -80 j m/s. Probably has some substitution of the Potential Energy (e) = m*h so m=e/h or something. Should get you going in the right direction

Answer 4

strictly speaking...ignoring air resistance...the 6.2kg object would technically hit first...Lets pretend that we are dropping the the bodies from the same height but on opposite sides of the planet...

Well Fg=G(m1*m2)/r^2...The earth will fall to the 6.2kg object at a higher rate than it would fall toward the 1.8g object...

but the high school answer is g*t=(9.8)(1.2)=11.76 m/s for both