Question

6. The speed of a body reduces from 90 km/h to 36 km/h. If the mass of the body is 50 kg, find the change

in its kinetic energy.​

Answer 1

ANSWER: change in kinetic energy is equal to final kinetic energy- initial kinetic

Hence KE = ½mv² - ½mv²

=½ × 50 × (10)² - ½ × 50 × (25)²

= 2500- 15625 => 13125 J or 13.125 KJ

neglect negative sign because KE can't be negative take only magnitude.

Answer 2

Explanation:

$\tt \: Initial \: \: speed \: u = 90km \: hr = \cancel{90} \times \frac{5}{ \cancel{18} } = 25 \: m \: sec \\ \tt \: Final \: value \: v = \cancel{36 }\times \frac{5}{ \cancel{18} } = 10 \: m \: sec \\ \tt \: Now \: change \: in \: KE = \frac{m {v}^{2} }{2} - \frac{m {u}^{2} }{2} \\ \tt \: Change \: in \: KE = \frac{50 \times {25}^{2} }{2} - \frac{50 \times {10}^{2} }{2} \\ \tt\triangle \:KE = 13125 \: J$