What's the example you are talking about?
Balance them that's the reason why
Answer:
4.8 m/s
Explanation:
When she catches the train,
- They will have travelled the same distance.and
- Their speeds will be equal
The formula for the distance covered by the train is
d = ½at² = ½ × 0.40t² = 0.20t²
The passenger starts running at a constant speed 6 s later, so her formula is
d = v(t - 6.0)
The passenger and the train will have covered the same distance when she has caught it, so
(1) 0.20t² = v(t - 6.0)
The speed of the train is
v = at = 0.40t
The speed of the passenger is v.
(2) 0.40t = v
Substitute (2) into (1)
0.20t² = 0.40t(t - 6.0) = 0.40t² - 2.4 t
Subtract 0.20t² from each side
0.20t² - 2.4t = 0
Factor the quadratic
t(0.20t - 2.4) = 0
Apply the zero-product rule
t =0 0.20t - 2.4 = 0
0.20t = 2.4
(3) t = 12
We reject t = 0 s.
Substitute (3) into (2)
0.40 × 12 = v
v = 4.8 m/s
The slowest constant speed at which she can run and catch the train is 4.8 m/s.
A plot of distance vs time shows that she will catch the train 6 s after starting. Both she and the train will have travelled 28.8 m. Her average speed is 28.8 m/6 s = 4.8 m/s.
Answer:
Explanation:
Assuming there is only force in the y-component, the total net force acting on the parachute and the sky diver is:
(1)
Where:
is the drag force acting upwards
is the weight of the sky diver acting downwards, hence with negative sign
Then:
(2) This is the total net force excerted on the system parachute-sky diver, and the fact it is positive means is upwards
Now, according Newton's 2nd Law of Motion the force is directly proportional to the mass and to the acceleration of a body:
(3)
Where is the mass of the diver.
Substituting the known values and finding :
(4)
(5)
Finally:
This is the acceleration of the sky diver. Note it has a positive sign, which means its direction is upwards.