A block of mass 5 kg is resting on a smooth surface. At what angle a force of 20 N be acted on the body so that it will acquired a kinetic energy of 40 J after moving 4 m ?

Question

A block of mass 5 kg is resting on a smooth surface. At what angle a force of 20 N be acted on the body so that it will acquired a kinetic energy of 40 J after moving 4 m ? (A) 30° (B) 45° (C) 60° (D) 120°

Tardigrade Admin · Accepted Answer

According to work-energy theorem W= Change in kinetic energy F S cos θ=(1/2) m v2-(1/2) m u2 Substituting the given values, we get 20 × 4 × cos θ=40-0 (∵ u=0) or cos θ=(40/80)=(1/2) or θ= cos -1((1/2))=60°

Q. A block of mass $5 k g$ is resting on a smooth surface. At what angle a force of $20 N$ be acted on the body so that it will acquired a kinetic energy of $40 J$ after moving $4 m$ ?

$3 0^{\circ}$

$4 5^{\circ}$

$6 0^{\circ}$

$12 0^{\circ}$

According to work-energy theorem $W =$ Change in kinetic energy
$FS cos θ = \frac{1}{2} m v^{2} - \frac{1}{2} m u^{2}$
Substituting the given values, we get
$20 \times 4 \times cos θ = 40 - 0 (∵ u = 0)$
or $cos θ = \frac{40}{80} = \frac{1}{2}$ or
$θ = cos^{- 1} (\frac{1}{2}) = 6 0^{\circ}$

Q. A block of mass 5kg is resting on a smooth surface. At what angle a force of 20N be acted on the body so that it will acquired a kinetic energy of 40J after moving 4m ?

30∘

45∘

60∘

120∘