<span>A baseball speeds up as it falls through the air.
Yes. Forces on the balloon are unbalanced.
The balloon is speeding up, so we know that the downward force
of gravity is stronger than the upward force of air resistance.
A soccer ball is at rest on the ground.
No. The ball is not accelerating, so we know that the forces on it
are balanced.
The downward force of gravity on the ball and the upward force
of the ground are equal.
An ice skater glides in a straight line at a constant speed.
No. The skater's speed and direction are not changing, so he is not
accelerating. That tells us that the forces on him are balanced.
A bumper car hit by another car moves off at an angle.
Yes. The direction in which the car was moving changed.
That's acceleration, so we know that the forces on it are unbalanced,
at least at the moment of impact.
A balloon flies across the room when the air is released.
Yes. The balloon was not moving. But when the little nozzle was
opened, it started to zip around the room. So its speed changed.
And, as it goes bloozing around the room, its direction keeps changing too.
There's a whole lot of acceleration going on, so we know the forces on it
are unbalanced.</span>
I calculated on a sheet and used differentiation to solve the problems.
The answer would be D.) Nebula
Answer:
t ’= 
, v_r = 1 m/s t ’= 547.19 s
Explanation:
This is a relative velocity exercise in a dimesion, since the river and the boat are going in the same direction.
By the time the boat goes up the river
v_b - v_r = d / t
By the time the boat goes down the river
v_b + v_r = d '/ t'
let's subtract the equations
2 v_r = d ’/ t’ - d / t
d ’/ t’ = 2v_r + d / t
In the exercise they tell us
d = 1.22 +1.45 = 2.67 km= 2.67 10³ m
d ’= 1.45 km= 1.45 1.³ m
at time t = 69.1 min (60 s / 1min) = 4146 s
the speed of river is v_r
t ’= 
t ’=
In order to complete the calculation, we must assume a river speed
v_r = 1 m / s
let's calculate
t ’= 
t ’= 547.19 s
