The concept of impulse is particularly useful in estimating average force in an

Question

The concept of impulse is particularly useful in estimating average force in an interaction. Follow the calculations below to see how impulse is related to other physical quantities a. Study of olympic boxers show that punch of a boxer can produce a force in the range of 3400 newtons. If the contact of the punch lasts 0.14 second (about half of typical human reaction time), estimate the impulse delivered by a boxer's punch. Impulse delivered by a boxer's punch is newton-second. b. Sometimes, we don't know the forces involved in the interaction, but instead, we know the initial and final velocities of the objects involved in the interaction. Consider baseball for example. Suppose a batter hits a fastball approaching at 45 m/s and the ball flies away at 53 m/s. The mass of a baseball is 0.145 kg. What is the magnitude of the impulse delivered to the baseball by the bat? Hint (b) The magnitude of the impulse delivered to the baseball by the bat is kilogram meter/second. c. We can compare these two interactions on the basis of impulse (see above), but sometimes, we are more interested in the forces (human body can withstand very large amount of impulse, if it's delivered over a long time with small forces, but we cannot withstand very large forces lasting over more than a few milliseconds, delivering relatively small impulse). In order to estimate average force from impulse, we need the duration of interaction. Suppose that the contact of the bat with the baseball in (b) lasts for 0.7 milliseconds. What is the magnitude of the average force that the bat exerts on the baseball, for the duration of contact? Hint (c) The magnitude of the average force is * newtons

Explanation / Answer

Impulse - Impulse is defined as the product of a force times the duration of its contact with an object. An impulse is simply “change in momentum”. Impulse is a vector and the unit is the Newton-second (Ns).

a) Impulse = 3400*0.15 N.s = 510 N.s

b)impulse = change in momentum = final momentum - initial momentum

therefore, impulse = mvf - mvi

from question vi = 45 m/s , vf = -53 m/s (negative since opposite to vi) , m= 0.145 Kg

hence, Impulse delivered to the baseball by the bat = m(vf - vi) = 0.145 (53+45) = 14.21 N.s

c) time of contact = 0.7 ms = 0.7 x 10-3 s

Impulse = Force x time of contact

14.21 N.s = Force x (0.7 x 10-3 s)

Force = 20.3 x 103 N

Average Force = 20,300 N

In case of any doubt, please comment sir.

Thank you.

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