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

                                 Or

                  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.

b)All you need to do is transpose for force and then solve. When done transposing you should get:

Solving physics equations can be tormenting if you don't know what you are doing and some can be very disturbing seeing how complicated some can get. So here I'll be showing you some tips for understanding calculations in physics.

1. First you need to know your formulas and how a specific formula is related to the question you are doing. 
2. Write down the quantities that you are given. This way you will know what formula to use for the question.
3. Practise alot of physics questions this way you'll be able to solve more difficult questions easily.
4. Please ensure you know your math very well, seeing that both subjects are interrelated. You must be able to transpose and make one term the subject of a formula because in almost every physics question there is going to be some type of transposition.
5. Ask for help whether online or at school. When you are unable to answer a question don't be afraid to ask, you would be surprised at how well this could turn out.