# Can rapid acceleration have momentum?

1. Jul 23, 2004

### BillyJohnson1992

A top fuel dragster can accelerate from 0 to 300mph in 4 seconds.

Scenario 1: Top fuel dragster is driving at a constant speed of 300mph. Driver cuts the fuel delivery to the engine. The speed will immediately decrease.

Scenario 2: Top fuel dragster is accelerating violently, at the 1 second mark the speed is already 100mph and going up at a dramatic pace. Driver cuts the fuel delivery to the engine. Will the speed immediately decrease?

Help!!

2. Jul 23, 2004

### gerben

Yes, it will slow down at the moment the engine does not deliver force on the wheels anymore, and if it gets no fuel the engine cannot exert any force.

Momentum is velocity times mass. An object will keep the same momentum as long as no force is acting on it. There are different kinds of friction forces acting on the dragster and when it is speeding up (and its momentum is increasing) the force between the wheels and the ground is larger than the friction forces (air friction, friction in parts of engine and bearings). Those friction forces will slow the dragster down when there is no forward force.

3. Jul 25, 2004

### Gza

The fact that the dragster in Scenario 2 had a period of acceleration before it's period of deceleration doesn't change the physics of the situation. The velocities decrease at the same rate if all other factors are held constant.

4. Jul 25, 2004

### JohnDubYa

... as long as no net external force is acting on it.