How Do Forces Affect Motion in Different Scenarios?

[willingtolearn]

#1
On takeoff, the combined action of the engines and wings of an airplane exerts an 8000N force on the plane, directed upward at an angle of 65* above the horizontal. The plane rises with constant velocity in the vertical direction while continuing to accelerate in the horizontal direction.
a) What is the weight of the plane ?
b) What is its horizontal acceleration ?
-------------------------------
V (initial)= 0
weight = mass time gravity
weight = 9.8 time mass
acceleration in vertical direction = 0 (constant speed)
F (apply) = 8000 N
From F = ma --> m = F / a
And I stuck at this point !


#2
Two blocks are fastened to the ceiling of an elevator. Each block is 10 kg. The elevator accelerates upward at 2 m/s2 (at the block that close to the ceiling). Find the tension in each rope.
------------------------------

F (upper) = 100 N
F (lower) = 100 * 2 = 200 N


#3
A 72 kg man stands on a spring scale in an elevator. Starting from rest, the elevator ascends, attaining its maximum speed of 1.2 m/s in .80s. It travels with this constant speed form 5 s, undergoes a uniform negative acceleration for 1.5 s and comes to rest. What does the spring scale registered (a) before the elevator starts to move ? (b) during the first .8 s ? (c) while the elevator is traveling at constant speed ? (d) during the negative acceleration ?
--------------------------------
a) Weight = 72*9.8 = 705.6 N because Fg = m*g
b) From V (intial) = 0 V (final) = 1.2 m/s t = .8 s
so a = 1.5 m/s2.
F = 705.6 + F (that is accelerating) ==> 705.6 + 72 (1.5) = 813.6 N
c) 705.6 N
d) I don't get what is this say "undergoes a uniform negative acceleration for 1.5 s and comes to rest"

Help Please ? Thanks

 

[Hootenanny]

#1
On takeoff, the combined action of the engines and wings of an airplane exerts an 8000N force on the plane, directed upward at an angle of 65* above the horizontal. The plane rises with constant velocity in the vertical direction while continuing to accelerate in the horizontal direction.
a) What is the weight of the plane ?
b) What is its horizontal acceleration ?
-------------------------------
V (initial)= 0
weight = mass time gravity
weight = 9.8 time mass
acceleration in vertical direction = 0 (constant speed)
F (apply) = 8000 N
From F = ma --> m = F / a
And I stuck at this point !

Hints;

1. How much force is airplane exerting vertically
2. How much force is it exerting horizontally

#2
Two blocks are fastened to the ceiling of an elevator. Each block is 10 kg. The elevator accelerates upward at 2 m/s2 (at the block that close to the ceiling). Find the tension in each rope.
------------------------------

F (upper) = 100 N
F (lower) = 100 * 2 = 200 N

I'm not sure how you've calculated 100N, but it's wrong.

#3
A 72 kg man stands on a spring scale in an elevator. Starting from rest, the elevator ascends, attaining its maximum speed of 1.2 m/s in .80s. It travels with this constant speed form 5 s, undergoes a uniform negative acceleration for 1.5 s and comes to rest. What does the spring scale registered (a) before the elevator starts to move ? (b) during the first .8 s ? (c) while the elevator is traveling at constant speed ? (d) during the negative acceleration ?
--------------------------------
a) Weight = 72*9.8 = 705.6 N because Fg = m*g
b) From V (intial) = 0 V (final) = 1.2 m/s t = .8 s
so a = 1.5 m/s2.
F = 705.6 + F (that is accelerating) ==> 705.6 + 72 (1.5) = 813.6 N
c) 705.6 N
d) I don't get what is this say "undergoes a uniform negative acceleration for 1.5 s and comes to rest"

Answers (a) through (c) are correct. (d) simply means decceleration.

 

[willingtolearn]

Can you give me some hints for problem 2 please ?

 

[Faster_Gun]

Sorry to bring up an old dead topic but I just got problem 3 for homework. What I did for d:
Find acceleration: a=(0Vf-1.2Vo(top speed of elevator ascending))/1.5time stated = -.8.
Net force = 705.6Normal weight+((72mass)x(-.8acceleration)) = 648N

Any mistakes?