2.6 Understanding Impulse and Impulsive Force Force and Motion 2.6 Understanding Impulse and Impulsive Force

IMPULSE Is defined as the product of a force, F acting on an object of mass, m for time ,t Impulse = Force x Time Impulse = Ft Also can be define as the change of momentum Impulse= mv – mu Impulse ,Ft = mv – mu Unit kgms-1 or Ns Is a vector quantity

IMPULSIVE FORCE Large force that acts over a short period of time during collision or explosion Also can be define as the rate of the change of momentum in a collision or an explosion Formula : F = mv – mu t Unit kgms-2 or N Example involving impulsive force: Football Playing golf Playing baseball Playing tennis Playing badminton

Example 1:

Solution

Example 2

Solution

INCREASING THE TIME IMPACT TO REDUCE THE IMPULSIVE FORCE

DECREASING THE TIME IMPACT TO INCREASE THE IMPULSIVE FORCE

Exercise 1 A boy hits a 0.50kg ball and sends it moving the opposite direction. Figure shows the magnitudes of its velocity before and after being hit respectively. The time of contact between the land and the ball is 0.05s. 15 ms-1 20 ms-1 Calculate : The impulse applied to the ball. The impulsive force exerted on the ball by the hands.

Exercise 2 A 300g ball is thrown horizontally towards a vertical wall at a velocity of 12ms-1. On impact, the ball bounces back horizontally at a velocity of 10ms-1. If the ball is in contact with the wall for 0.02s, find: The impulse The force exerted on the ball.

Exercise 3 Figure shows a 2kg wooden block initially at rest on a smooth surface. A force of 8N is applied on the wooden block. If the force acts for 3s: What is the impulse on the block What is the velocity of the wooden block after 3s? 2 kg 8 N u = 0 v t = 0s t = 3s

Exercise 4 A tennis ball and a piece of mud with the same mass ( 0.060 kg) and moving at 9ms-1 both strike a wall. The mud sticks to the wall while the ball rebounds at 6 ms-1. Find the impulse on each object. 9ms-1 Mud Tennis ball 9ms-1 6 ms-1