Question

Convert each of the following to three significant figures: (a) 20 lb.ft to N.m, (b) 450 Ib/ft^3 to kN/m^3, and (c) 15 ft/h to mm/s.

Answer 1

a)20 lb.ft=27.2 N.m

b)
`450(lb)/(ft^3)=70.65(KN)/(m^3)`

c)15 ft/h = 1.26 mm/s

Step-by-step explanation:

a)

As we know that

1 ft.lb= 1.36 N.m

So 20 lb.ft = 1.36 x 20 N.m

20 lb.ft=27.2 N.m

b)

We know that

`1(lb)/(ft^3)=0.157(KN)/(m^3)`

So

`450(lb)/(ft^3)=450* 0.157(KN)/(m^3)`

`450(lb)/(ft^3)=70.65(KN)/(m^3)`

c)

As we know that

1 ft/h=0.084 mm/s

So

15 ft/h = 0.084 x 15 mm/s

15 ft/h = 1.26 mm/s

Answer 2

(a)27.12 N-m (b) 69.96
`KN/m^3` (c) 1.27 mm/sec

Step-by-step explanation:

We have to convert

(a) 20 lb-ft to N-m

We know that 1 lb = 4.45 N

So 20 lb = 20×4.45 = 89 N

1 feet = 0.3048 m

So
`20lb-ft=20* 4.45N* 0.3048N=27.12N-m`

(b) 450
`lb/ft^3` to KN/
`m^3`

We know that 1 lb = 4.45 N = 0.0044 KN

`1ft^3=0.0283m^3`

So
`450lb/ft^3=(450* 0.0044KN)/(0.0283m^3)=69.96KN/m^3`

(c) 15 ft/hr to mm/sec

We know that 1 feet = 0.3048 m = 304.8 mm

And 1 hour = 60×60=3600 sec

So
`15ft/h=(15* 304.8mm)/(3600sec)=1.27 mm/sec`