U2-3-3-HW QUESTION 1 An 85,000 N spaceship comes in for a vertical landing on ea

Question

U2-3-3-HW QUESTION 1

An 85,000 N spaceship comes in for a vertical landing on earth.

Assume g is constant at 9.8 m/s2. Starting with an initial speed
of 1000 m/s it comes to rest in 2.4 minutes with uniform acceleration.
What braking force must its rockets provide? Ignore air resistance.
Take upward as the positive y-direction with the origin at the landing point.
Find all unknowns below. HINT: Draw all forces on the spaceship with the vector sum = may
SORT
Weight of spacecraft = _______N (positive)
Initial Y-position, yo : Need to find this in meters
Initial Y-velocity, Vyo =_______m/s
Y-acceleration, ay : Need to find this in m/s2

Final Y-position, yf = _______m
Final Y-velocity, Vfy = _______m/s
Elapsed time, t = _______SECONDS

QUESTION 2

GUESSTIMATE

If the spaceship were hovering, what would be the UPWARD force on the ship?

0 N

Weight of the ship

twice the weight of the ship

The Weight x 9.8

QUESTION 3

GUESSTIMATE
If the spaceship were hovering, what would be the acceleration on the ship?

0.0 m/s2

-9.8 m/s2

+9.8 m/s2

magnitude greater than 9.8 m/s2   

QUESTION 4

GUESSTIMATE
The acceleration of the spaceship when landing is

Positive (vfy - voy) / t > 0   

Zero (vfy - voy) / t = 0   

Negative (vfy - voy) / t < 0   

QUESTION 5

GUESSTIMATE
The force applied by the engines is ________ the spaceship's weight

less than

equal to

greater than

QUESTION 6

SOLVE
Initial position of the spaceship, Yo = _______meters

QUESTION 7

SOLVE
Acceleration of the spaceship, ay = ________m/s2

QUESTION 8

SOLVE
Braking force on ship supplied by its engines to slow and land ship, Fbraking = ______N
CHECK
Was the acceleration as expected? (No answer required here)
Was the force as expected? (No answer required here)

0 N

Weight of the ship

twice the weight of the ship

The Weight x 9.8

Explanation / Answer

a)

Braking force required = m*(v - u)/(t)

= (85000/9.8)*(1000 - 0)/(2.4*60)

= 60232 N

b)

For hovering,

weight of the spacecraft = upward force

So, answer is : weight of the spacecraft

c)

If the ship was hovering, acceleraion = 0

d)

when landing , a =   (vfy - voy) / t < 0

Value of a comes to be negative as Vf = 0

e)

acceleration =   (vfy - voy) / t

= (0 - 1000)/(2.4*60)

= -6.94 m/s2

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