8/13/2019 EGR280 Mechanics 12 WorkAndNRG

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8/13/2019 EGR280 Mechanics 12 WorkAndNRG

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12.4 ,he (0-lb load is hoisted by the

p*lley system and the motorM. f themotor e4erts a constant force of 0 lb

on the cable" determine the power that

m*st be s*pplied to the motor if the

load has been hoisteds

10 ft startingfrom rest. ,he motor has an efficiency

of 0./%.

Ans: 5 1.% hp

12.5 ,he collar has a weight of 3 lb. f

it is released from rest at a height of h2 ft from the top of the *ncompressed

spring" determine the speed of the collar

after it falls and compressed the spring

0. ft.

Ans: v2 11./ ft's

12.6 ,he 2-lb block is given an initial

velocity of 20 ft's when it is atA. f the

spring has an *nstretched length of 2 ftand a stiffness of k 100 lb'ft"

determine the velocity of the block

whens 1 ft.

Ans: vC 16.& ft's

12.7 ,he 2-kg ball of negligible sie isfired from point ! with an initial

velocity of 10 m's *p the smooth slope.

Determine the distance from point to

where it hits the horiontal s*rface at D.!lso" what is its velocity when it strikes

the s*rface#

Ans: d 3.( m" vD 10 m's