# A 1600 kg jet engine is fastened to the fuselage of a passenger jet

1. Feb 19, 2012

### sb13

1. The problem statement, all variables and given/known data

A 1600 kg jet engine is fastened to the fuselage of a passenger jet by just three bolts (this is the usual practice). Assume that each bolt supports one-third of the load. (a) Calculate the force on each bolt as the plane waits in line for clearance to take off. (b) During flight, the plane encounters turbulence, which suddenly imparts an upward vertical acceleration of 2.0 m/s2 to the plane. Calculate the force on each bolt now.

2. Relevant equations

F= ma

3. The attempt at a solution

I got the correct solutions for both (a) and (b)

(a) F=ma= (1600 kg)(9.8 m/s^2) = 15680 N/3= 5226.67 N

(b) F=ma= (1600 kg)(9.8 m/s^2 + 2.0 m/s^2) = 18880 N/3 = 6293.33 N
But on (b), I don't understand why the acceleration of gravity was added to the upward vertical acceleration of 2.0 m/s^2, isn't gravity pulling the plane down, and the 2.0 m/s^2 pulling it up, shouldn't it be 9.8-2.0?

2. Feb 19, 2012

### LawrenceC

Re: Forces

Because the plane is accelerating upward, the engine 'weighs' more due to its acceleration upward. The force due to an acceleration is in the opposite direction of the acceleration.

3. Feb 19, 2012

### sb13

Re: Forces

Ok. So the gravitational force ends up creating a greater force and because the acceleration is going upward, it is causing more force as well? What is the acceleration was -2.0 m/s^2 and the plane was being pulled downward, what effect would that have on the engine's force?

4. Feb 19, 2012

### GothFraex

Re: Forces

Think about this, when an elevator is accelerating upwards you feel heavier. The elevator is pulling you upwards but you feel a stronger downward force. Similarly when the elevator is accelerating downwards you feel lighter.

5. Feb 19, 2012

### LawrenceC

Re: Forces

If the plane is accelerating downward, then the force due to acceleration points upward. The gravitational force is the same. It's the force due to acceleration of the plane that causes the change in the load of the bolts.

Gravitational force exists and is the same whether the plane is moving or stopped. The acceleration of the plane either adds to it or subtracts from it.