Question

A block of mass 10 kg is moving in x – direction with a constant speed 10 ms^-1. It is subjected to a retarding force F = -0.1 x J/m during its travel from x = 20 m to x = 30 m. Find the final KE.

• A. 475 J
• B. 450 J
• C. 275 J
• D. 250 J

Answer 1

Answer: (A)

475 J

Answer 2

KE_f = $\int _ { 20 } ^ { 30 } \mathrm {~F} . \mathrm { dx } + \mathrm { KE } _ { \text {initial } }$

= $\int _ { 20 } ^ { 30 } - ( .1 ) \mathrm { xdx } + \frac { 1 } { 2 } \times 10 \times 10 ^ { 2 }$

= $\left[ \frac { - 30 ^ { 2 } } { 2 } + \frac { 20 ^ { 2 } } { 2 } \right]$ (.1) + 500. = 475 J