Question

How much work must be done by a force on 50 kg body in order to accelerate it from rest to 20 $ms^{-1}$ in 10 s

• A. $10^3 J$
• B. $10^4 J$
• C. $2 \times 10^3 J$
• D. $4 \times 10^4 J$

Answer 1

Answer: (B)

$10^4 J$

Answer 2

Final velocity v = u + at $\therefore$ $20 =0 +a \times 10$ or $20 =a \times 10$ or $a=2 ms^{-2}$ now $s=ut+\frac{1}{2}at^2$ or $s=0+\frac{1}{2}\times 10 \times 10 \times$ or s=100m $\therefore$ work done W = F $\times$ s or W = ma $\times$ s $\therefore$ $W=50 \times 2 \times 100 \,or\,W =10000$ $=10^4J$