A 9 kg sledge hammer head is initially moving downward at 5 m/s and eventually c

ID: 777625 • Letter: A

Question

A 9 kg sledge hammer head is initially moving downward at 5 m/s and eventually comes to

a rest after hitting a concrete cinder block.

a) Calculate the magnitude of the impulse to the hammer head while coming to a stop

b) If the block does not break, the hammer head comes to a stop in only 0.02 seconds. What is the

magnitude of the average net force acting on the block while it comes to a stop in this case?

c) If the block does break, the hammer head comes to a stop in over a longer time of 0.22 seconds. What

is the magnitude of the average net force acting on the block while it comes to a stop in this case?

Mass of the sledge hammer m = 9 kg

Initial velocity of the hammer u = 5 m/s

Final velocity of the hammer v = 0

Change in the velocity of the hammer v = v - u

= 0 - 5

= - 5 m/s

Impulse on an object is equal to the change in momentum of the object.

I = P = ( mv ) = m v ................ ( 1 )

a) Impulse to the hammer I = m v

= 9 × ( - 5 )

= - 45 kg m/s

Negative sign indicates that momentum of the hammer decreases

Magnitude of the Impulse to the hammer is I = 45 kg m /s

b) Impulse on an object is defined also as the product of the average force and time interval in which force acts.

I = Favg × t

Favg = I / t

Time interval in which hammer comes to rest is t = 0.02 s

Magnitude of the average force acting on the block

Favg = I / t

= 45 / 0.02

= 2250 N

C) Time interval in which hammer comes to rest is t = 0.22 s

Average force acting on the block is

Favg = I / t

= 45 / 0.22

= 204.54 N

So average force acting on the block is Favg = 204.54 N

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