Answer:
10 newtons, because the gravitaional force willbe stronger the closer it gets.
I believe the correct answer from the choices listed above is option C. The instrument that is <span>best suited for measuring the dimensions of a shoebox would be a ruler. A triple-beam balance is for measuring mass. A volumetric flask is for volume. A caliper is measuring lengths of small objects.</span>
Via half-life equation we have:

Where the initial amount is 50 grams, half-life is 4 minutes, and time elapsed is 12 minutes. By plugging those values in we get:

There is 6.25 grams left of Ra-229 after 12 minutes.
the first step would be gathering information , and making sure its correct
M = mass of the first sphere = 10 kg
m = mass of the second sphere = 8 kg
V = initial velocity of the first sphere before collision = 10 m/s
v = initial velocity of the second sphere before collision = 0 m/s
V' = final velocity of the first sphere after collision = ?
v' = final velocity of the second sphere after collision = 4 m/s
using conservation of momentum
M V + m v = M V' + m v'
(10) (10) + (8) (0) = (10) V' + (8) (4)
100 = (10) V' + 32
(10) V' = 68
V' = 6.8 m/s