Question

A body dropped freely from certain height reaches the ground in 3 seconds. The ratio
of the
distances travelled by it in the last 3/4 second and last but one 3/4 second is
1) 3:5
2) 5:7
3) 7:5
4) 1:2
​

Answer 1

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11th

Physics

Motion in a Straight Line

Problems on Equation of Motion

A body is dropped from cert...

PHYSICS

A body is dropped from certain height H. If the ratio of the distances travelled by it in (n-3) seconds to (n-3)

th

second is 4 : 3, find H. (Take g = 10 m s

−2

)

MEDIUM

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ANSWER

S

n−3

=ut+

2

1

at

2

(u=0,a=g)

S

n−3

=

2

1

gt

2

=

2

1

g(n−3)

2

S

n

th

=u+

g

a

(2n−1) [distance traveled in n

th

second with constant acceleration]

S

(n−3)

th

=

2

g

(2(n−3)−1)

=

2

g

(2n−7)

S

n−3

th

S

n−3

=

2×

2

g

×(2n−7)

g(n−3)

2

=

3

4

3(n

2

+9−6n)=4(2n−7)

3n

2

+27−18n=8n−28

3n

2

−26n+55=0

3n

2

−15n−11n+55=0

3n(n−5)−11(n−50=0

n=5,

3

11

H=

2

1

g(5)

2

H=125m

Explanation:

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