Correct Option: B

Let the body fall through the height of tower in t seconds. From,
D_n = u + (a/2) 2n - 1 we have, total distance travelled in last 2 seconds of fall is
D = D_t + D(_t-1)

		0 +	g	(2t - 1)		+		0 +	g	{2(t - 1) - 1}
			2						2

=	g	(2t - 1) +	g	(2t - 3) =	g	(4t - 4)
	2		2		2

=	10	× 4(t - 1)
	2

or,  40 = 20 (t – 1) or t = 2 + 1 = 3s
Distance travelled in t seconds is

s = ut +	1	at² = 0 +	1	× 10 × 3² = 45m
	2		2