# Rocket Physics Launching Force

A 1 Kg rocket is launched upwards with a force of 9.8N. What happens to this rocket ?

g = 9.8 m/s^2

A) Never takes off the ground

B) Lifts of at a constant velocity

C) Accelerates initially and then drops down

D) Other

E) What would happen at greater accelerations

Your detailed thoughts please!

Â© BrainMass Inc. brainmass.com December 24, 2021, 9:17 pm ad1c9bdddfhttps://brainmass.com/physics/newtons-third-law/rocket-physics-launching-force-363697

## SOLUTION This solution is **FREE** courtesy of BrainMass!

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Before the launch

The gravitational force on the rocket is a constant force pointing down. The only thing that stops the rocket from from moving down is the force exerted on the rocket by the ground (Newton's third law). This force applied by the ground is there as long as the rocket pushes on the ground.

Hence the before the launch the rocket is standing still.

The Launch

Now we apply on the rocket a force equal in magnitude to its gravitational weight but opposite in direction. The rocket than stops pushing on the ground, so there s no force applied on the rocket by the ground.

The total force on the rocket is zero - the gravitational force pints down while the launch force with equal magnitude points up.

Newton's first law states that "An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force"

The force here is balanced and the initial velocity is zero - the rocket is at rest and therefore will stay at rest.

The rocket will not take off the ground.

If we apply a a greater force (higher acceleration), then the net force acting on the rocket will not be zero anymore but rather some magnitude pointing upwards.

Then Newton's second law comes into play. This law states that the change in momentum equals the net force applied on the object. A change in momentum means that the velocity of the object has changed (at least if the mass stays the same). A change in velocity means that the body accelerates.

Therefore, if we apply a constant force larger than 9.8N upwards, the net force on the rocket will be positive (pointing upwards) and the rocket will accelerates upwards with constant acceleration.

The magnitude of this acceleration will be (again, assuming the mass of the rocket is constant):

a = (F-Mg)/M = (F/M) - g

Â© BrainMass Inc. brainmass.com December 24, 2021, 9:17 pm ad1c9bdddf>https://brainmass.com/physics/newtons-third-law/rocket-physics-launching-force-363697