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

Answer:

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

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 $20lb-ft=20\times 4.45N\times 0.3048N=27.12N-m$

(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 $450lb/ft^3=\frac{450\times 0.0044KN}{0.0283m^3}=69.96KN/m^3$

(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 $15ft/h=\frac{15\times 304.8mm}{3600sec}=1.27 mm/sec$

Answer 2

Answer:

a)20 lb.ft=27.2 N.m

b)$450\dfrac{lb}{ft^3}=70.65\dfrac{KN}{m^3}$

c)15 ft/h = 1.26 mm/s

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

$1\dfrac{lb}{ft^3}=0.157\dfrac{KN}{m^3}$

So

$450\dfrac{lb}{ft^3}=450\times 0.157\dfrac{KN}{m^3}$

$450\dfrac{lb}{ft^3}=70.65\dfrac{KN}{m^3}$

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