Impulse: Calculations and Definitions

What is Impulse?
Impulse can be defined as the force per unit time or change in momentum. Momentum is changed whenever a force is applied to a body. From these definitions one can already see what formulas are in relation to impulse.

Formulas associated with Impulse:

Impulse = Force x Time

Impulse = Change in momentum = mV – mU

Where ‘m’ is Mass and V, U is final and initial velocity respectively.

Below are some calculations involving impulse. Here you’ll be using the formulas above to find the missing variable.

Example 1.
A force of 100 N is applied for 8 seconds. What is the impulse?

Answer:
Right away you can easily solve for impulse using the first formula above because all other variables are given.

   Therefore Impulse = Force x Time
   = 100N x 8sec
   = 800Ns

Example 2.
An impulse of 250Ns is applied for 10 seconds. What is the applied force?

Answer:
Again you can see that you have to use the first formula above, but in this case they gave values for impulse and time, therefore all you have to do is transpose the formula to make Force the subject and then solve for Force.

Example 3.

A body of 4kg is moving at 5m/s when it is given an impulse of 8Ns in the direction of the motion.

a) What is the Velocity of the body immediately after the impulse?
b) If the impulse acts for 0.02 seconds. What is the average value of the force exerted?

Answers:
a) Here they gave you mass (4kg), initial velocity (5m/s) and impulse (8Ns). Therefore all you need to do is transpose the second formula, which relates impulse to momentum, to make the final velocity(V) the subject of the formula and then solve.