Question

A 5 kg block is lifted vertically through a height of 5 metre by a force of 60 N.
Determine:
(i) The work done by applied force in lifting the block,
(ii) The potential energy of the block at 5 m,
(iii) The kinetic energy of the block at 5 m,
(iv) The velocity of the block at 5 m.

• A. $300J,245J,55J,4.69m/s$
• B. $200J,245J,50J,4.69m/s$
• C. $150J,150J,50J,4.69m/s$
• D. $300J,245J,100J,10.69m/s$

Answer 1

Answer: (A)

$300J,245J,55J,4.69m/s$

(i) W.D by applied force,
$w_f=f_s=60\times 5=300J$
(ii) change in PE,
$PE=mgh=5\times 9.8\times 5=245J$
(iii) KE$=W.D.$ by resultant force,
$=w_g+w_f$
$=-245+300=55J$
(iv) velocity since $KE=55$,
$V=\sqrt{\frac{55\times 2}{5}}=4.69m/s$