LINEAR MOMENTUM
1. LINEAR MOMENTUM
1.1 Linear Momentum (p) The quantity of motion contained in the body is linear momentum. It is given by the product of mass and the velocity of the body. It is a vector and its direction is the same as the direction of the velocity. momentum = mass x velocity
p = mv
For example, a fast-moving cricket ball has more momentum than a slow-moving one. But a slow-moving heavy roller has more momentum than a fast cricket ball.
1.1.2 Units of momentum:
The SI unit is kg · m/s, i.e., kg · m/s-1.
Dimension formula = [M1L1T-1].
1.1.3 Examples
1. A body of mass 3kg moves with a velocity of 10ms-1. Calculate the momentum of the body.
2. Calculate the momentum of each of the following objects:
a) a 0.50kg stone travelling at a velocity of 20ms−1
b) a 2000kg bus travelling at 20ms−1 on a road
c) an electron travelling at 2.0 × 107ms−1. (The mass of the electron is 9.1 × 10−31 kg.)
3. A force of 100N is used to kick a football of mass 0.8kg. Find the velocity with which the ball moves if it takes 0.8s to be kicked.
1.1.4 Change in momentum
Unbalanced force causes an object to move or accelerate, either speeding up or slowing down. If the force acts opposite to the motion of the object, it slows down, but if it acts in the same direction as that of the object, it increases the motion. Therefore, either way forces changes in the velocity of the object. When this occurs, we say that the momentum of the object changes. Change in momentum can be dangerous; for example, if a car were to have an accident, it has the tendency to reduce the large momentum of passengers to zero momentum, such as injuries, death, tiredness etc.