Under what circumstances would the roller skate and the truck have the same momentum ?
The roller skate and truck can have the same momentum if the product of the mass and velocity of the skate equal the product of the mass and velocity of the truck.
A 1000 kg truck moving at 0.01 m/sec has the same momentum as a 1 kg skate moving at 10 m/sec. Both have a momentum of 10 kg m/sec. ( 1000 x .01 = 1 x 10 = 10 )
If the time of impact is increased by 100 times (say from .01 sec to 1 sec), then the force of impact is reduced by 100 times (say to something survivable).
EXAMPLES :
padded dashboards on cars
airbags in cars
safety nets in circuses
moving your hand backward as you catch a fast-moving ball
flexing your knees when you land after jumping in the air
elastic cords for bungee jumping
using wrestling mats instead of hardwood floors.
dropping a glass dish onto a carpet instead of a sidewalk.
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