How Do You Calculate Upward Thrust and Force in Dynamics Problems?

[mardo]

Homework Statement

mass - 8150kg
acceleration upwards is 2m s-2
Thrust from engines - 98000N

Homework Equations

F=mg
F=ma

The Attempt at a Solution

I'm struggling with homework questions, below you can see exactly with which exercises I'm struggling.

Information, which has been given is:
mass = 8150kg

(a)Determine the upward thrust from its Rolls Royce engines whilst it is hovering, explaining how you have got your answer. How can I get upward thrust if I know only mass?

(b)The thrust from the Harrier’s engines is now increased so that it accelerates upwards at 2.0 m s-2 .
(i)Calculate the resultant upward force on the Harrier. How to get it?

(ii)At this instant the upward thrust of the engines is 98,000 N, calculate the air resistance acting on the Harrier as it accelerates upwards.

SECOND EXERCISE

I have also question about this point:


(c)The man continues pushing the trolley at 1.20 m s-1. However he is momentarily distracted and collides into a display of cut price Heinz baked beans exerting a force of approximately 50 N on the display.
What force was exerted by the display on the shopping trolley during the collision? Explain your answer.

It is normal contact force which has been exerted by the display, isn't it?

(d)How much force did the man have to apply to cause the trolley to speed up from rest to 1.20 m s-1 in 0.900 s, mass ir 28.00 kg

So if I use F=mg then I get 275N, is this the right answer?

 

[jbsteele]

For (a):The upward thrust from the Rolls Royce engines is given by F = ma, where F is the thrust, m is the mass, and a is the acceleration. Since we are given the mass of the Harrier (8150 kg) and the acceleration of the Harrier (2 m/s^2), we can calculate the thrust as 98000 N. For (b)(i):The resultant upward force on the Harrier is given by F=ma, where F is the force, m is the mass, and a is the acceleration. Since we are given the mass of the Harrier (8150 kg) and the acceleration of the Harrier (2 m/s^2), we can calculate the force as 163000 N. For (b)(ii):The air resistance acting on the Harrier as it accelerates upwards is given by F = ma, where F is the air resistance, m is the mass, and a is the acceleration. Since we know the thrust of the engines (98000 N) and the acceleration of the Harrier (2 m/s^2), we can calculate the air resistance as -385000 N.For (c):The force exerted by the display on the shopping trolley during the collision is 50N. This is because the display and the trolley are in contact and so they will exert equal and opposite forces on each other. For (d):The force required to cause the trolley to speed up from rest to 1.20 m/s in 0.900 s is given by F = ma, where F is the force, m is the mass, and a is the acceleration. Since we know the mass of the trolley (28.00 kg) and the acceleration of the trolley (1.33 m/s^2), we can calculate the force as 37.24 N.