A body falling freely under gravity passes two points 30 m apart in 1 s. From what point above the upper point it began to fall? (Take g= 9.8 m s-2).

Question

A body falling freely under gravity passes two points 30 m apart in 1 s. From what point above the upper point it began to fall? (Take g= 9.8 m s-2). (A) 32.1 m (B) 16.0 m (C) 8.6 m (D) 4.0 m

Tardigrade Admin · Accepted Answer

Suppose the body passes the upper point at

t

second and lower point at

(t + 1) s

, then

S_{2} - S_{1} = \frac{1}{2} g (t + 1)^{2} - \frac{1}{2} g t^{2}

= \frac{1}{2} g (2 t + 1)

or

30 m = \frac{1}{2} \times 9.8 (2 t + 1)

∴ t = 2.56 s

S_{1} = \frac{1}{2} g t^{2} = \frac{1}{2} \times 9.8 \times (2.56)^{2}

= 32.1 m

Q. A body falling freely under gravity passes two points $30 m$ apart in $1 s$ . From what point above the upper point it began to fall? (Take $g = 9.8 m s^{- 2}$ ).

$32.1 m$

$16.0 m$

$8.6 m$

$4.0 m$

Q. A body falling freely under gravity passes two points 30m apart in 1s. From what point above the upper point it began to fall? (Take g=9.8ms−2).

32.1m

16.0m

8.6m

4.0m

Suppose the body passes the upper point at t second and lower point at (t+1)s, then S2​−S1​=21​g(t+1)2−21​gt2 =21​g(2t+1) or 30m=21​×9.8(2t+1) ∴t=2.56s S1​=21​gt2=21​×9.8×(2.56)2 =32.1m

Q. A body falling freely under gravity passes two points $30 m$ apart in $1 s$ . From what point above the upper point it began to fall? (Take $g = 9.8 m s^{- 2}$ ).

$32.1 m$

$16.0 m$

$8.6 m$

$4.0 m$