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Impulse

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Presentation Outline

• Understanding concepts
  • Impulse
  • Average Force
• Example Problems
  • Problem 1 (11.1)
    • Solution Strategy
    • Work
  • Problem 2 (11.11)
    • Solution Strategy
    • Work
  • Problem 3 (11.13)
    • Solution Strategy
    • Work

Average Force

• More often than not, the force at each individual moment during a collision is not known. In this case, the time-average force is more useful:
• This relation gives a quick estimate of the average magnitude of the impulsive forces occurring during the collision, instead of trying to map out each change throughout the period of time during which the collision occurred.
• The SI standard units for average force are N, while the units for impulse are N-s or kg-m/s.

Example Problem 1

A stuntman of mass 77 kg “belly-flops” on a

shallow pool of water from a height of

11m. When he hits the pool, he comes to

rest in about .05 s. What is the impulse

that the water and the bottom of the pool

deliver to his body during this time

interval? What is the time-average force?

Example Problem 1 (Work)

• Part 1:
• Part 2:

Example Problem 2

A soccer player applies an average force of

180 N during a kick. The kick accelerates a

.45 kg soccer ball from rest to a speed of

18 m/s. What is the impulse imparted to

the ball? What is the collision time?

Example Problem 2 (Work)

• Part 1:
• Part 2:

Example Problem 3

The net force on a body varies with time

according to Fx=3.0t+0.5t^2 where Fx is in

Newtons and t is in seconds. What is the

impulse imparted to the body during the

time interval 0<t<3.0s?

Example Problem 3 (Work)

• Solution: