Question

a ball is thrown vertically upwards from the top of a tower with a speed of 100m/s it strikes the pond near the base of the tower after 25 second .the height of the tower is

Answer 1

height of tower is 625 m.
when he throw the ball and ball return till the height of tower it takes 20 sec. [T= 2u/g= 200/10 = 20sec]
rest 5 sec he take to cross tower's height. soheight of tower[h]= ut + 1/2 at2
   h = -100 * 5 + 1/2 *[-10] 5*5 = 625 m {height always +ve}

Answer 2

u=100m/s
v=0
t=25s
a=v-u/t
a=0-100/25
a=-4m/s^2
now,v^2=u^2+2gh
0^2=100^2+2×-4×h
-10000=-8h
10000/8=h
5000/4=h
2500/2=h
1250m=h

for verification----
h=ut+1/2at^2
1250=100×25+1/2×-4×25×25
1250=2500+(-50×25)
1250=2500-1250
1250=1250. ✓


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