Question

A force of 20 N acts on a Wooden block of 25 kg initially at rest. How long does the force take to displace the block through 1 hectameter and what is its velocity then? [3 MARKS]

Answer 1

Calculation : 1 Mark each

F = 20 N; M = 25kg; u = 0

S = 1hm = 100m

$t=?v=?$

$Step1:a=\frac{F}{M}=\frac{20}{25}m{s}^{-2}$

$Step2:s=\frac{1}{2}a{t}^2$

$s=\frac{1}{2}.\frac{F}{M}{t}^2$

$\therefore t^2=\frac{2\times S\times M}{F}$

$=\frac{2\times 100\times 25}{20}=250s^2$

$\therefore t=5\sqrt{10}=5\times 3.16=15.8s$

$Step3:v^2-u^2=2as$

$0+2\times \frac{20}{25}\times 100$

$=160$

$\therefore v=4\sqrt{10}=12.64m{s}^{-1}$