Which is not expecting acceleration?

A point on the outside of a spinning top whose rotational speed is constant.
A skydiver whose air resistance is equal to that of her weight.
A car on the freeway experiencing a net force of -120 N.
A submerged beach ball whose buoyant force is eight times the force of gravity on it.
Which is a valid internal frame of reference?

A frictionless spinning merry go round.

A falling rock.

A hot air balloon moving at 30 degrees east of north with no net force.

A space shuttle whose boosters just ignited for takeoff.

Two teams are playing tug of war. The team on the right is pulling with 4320 N. The team on the left is pulling with 4380 N. Which direction does the rope move and with what force?

60N to the right
120N to the left
60 N to the left
120 N to the right

1 answer

A skydiver whose air resistance is equal to that of her weight.
No net force so 0 = m a

No net force is a pretty strong hint

Oh come on you can do the tug of war.