Cracking the SAT Physics Subject Test

IMPULSE

The product of force and the time during which it acts is known as impulse, a term
you should be familiar for this test.

That Hurts!

Since concrete is hard

and has no cushion, the

impact time of any object

striking concrete is very

short. Forces that exist

over a short period of

time are called impulsive

forces. A large change in

momentum divided by a

short time interval makes

for a painful landing on a

concrete floor.

Impulse is a vector quantity that’s symbolized by J.

J = F∆t

Newton’s second law can be written in yet another form, in terms of

impulse.

J = ∆p

Sometimes this is referred to as the impulse–momentum theorem, but it’s just
another way of writing Newton’s second law.

2. A football team’s kicker punts the ball (mass = 0.42 kg) and
   gives it a launch speed of 30 m/s. Find the impulse delivered to the
   football by the kicker’s foot and the average force exerted by the
   kicker on the ball, given that the impact time is 0.0020 s.

Here’s How to Crack It

Impulse is equal to the change in linear momentum, so