Question

3.
A body starts from rest and is acted on by a
constant force. The ratio of kinetic energy gained
by it in the first five seconds to that gained in the
next five seconds is
1)2:1 2)1:1 3) 3:1 1:3​

Answer 1

Answer:

1:3

Explanation:

$KE = 1/2 MV^{2}$

For first 5 sec,

v = u + at

u = 0

V = a5

Thus, KE1 = $1/2 ma^{2}25$ this is KE gained in first 5 sec

For next 5 sec,

V= a10

KE = $1/2m(a10)^{2}$

KE2 = $1/2ma^{2} 10^{2} - 1/2ma^{2}5^{2}$ this is KE gained in next 5 sec

      = $1/2 ma^{2} 75$

$Thus,\\\frac{KE1}{KE2} = 25/75 = 1:3$ (rest part of KE is constant)