Newton's 2nd Law conceptual problem

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A 15,000 kg rocket blasts off from Earth with a uniform upward acceleration of 2.0 m/s2 and feels no air resistance. The thrust force its engines must provide during this acceleration is 30,000 N upward.

Apparently this is FALSE!

I don't understand why
F=MA
$$30000N=15000kg*2m/s^2$$

indeed the math is true?

why is the answer false? What am I missing? Thanks!

 

[cjl]

Because you have to also counter the rocket's weight, so the force must be equal to the rocket's weight plus an additional 30,000 N to cause a 2 m/s² upward acceleration.

(It might be easier to see if you draw a free body diagram)

 

[Sakha]

Expanding cjl's post:

$$30000N=15000kg*2m/s^2$$
is wrong; while
$$F=15000kg*(2m/s^2 + 9.8m/s^2)$$
is the right expression.

 

[MasterX]

Remember that F in Newton's 2nd law are all the forces that are acting on a body. Thus, besides the upward force, you also have a downward force, which is gravity.

 

[PJC01]

The answer is not false, but the statement may be misleading. Newton's second law states that the net force acting on an object is equal to its mass multiplied by its acceleration. In this case, the net force acting on the rocket is indeed 30,000 N, which is equal to 15,000 kg multiplied by 2 m/s^2. However, this does not mean that the rocket's engines are providing a thrust force of 30,000 N upward. The engines are actually providing a thrust force greater than 30,000 N in order to overcome the force of gravity and accelerate the rocket upward. Additionally, the statement does not take into account the fact that the mass of the rocket decreases as fuel is burned during liftoff, which affects the acceleration. So while the math may be correct, the statement oversimplifies the situation and does not accurately describe the forces at play during liftoff.