Question

40. A stone is dropped from a height of 20 m.
✓ 0 How long will it take to reach the ground?
(i) What will be its speed when it hits the ground ? (8 = 10 m/s2)
41. A stone is thrown vertically upwards with a speed of 20 m/s. How high will it go before it begins to fall ?
(8 + 9.8 m/s)​

Answer 1

Answer:

Height of stone is :- 20m

Time to reach the ground :- ?

We use the Equation:-

$s = ut + \frac{1}{2} a {t}^{2}$

S is displacement

u is initial velocity

t is the time

S = 20m

t = ?

u= 0 m/s. ( at the top the speed is zero of any object)

a =10m/s²

20=(0)×t +½ (10)(t)²

20= +½ 10t²

20=5t²

4=t²

t=2s

we have another formula:-

$a = \frac{v - u}{t}$

a = 10 m/s²

v = 0 m/s

u=?

t=2s

Substituting all the values in the formula we get.

$- 10 \frac{0 - u}{t}$

u= -20m/s

speed of the falling object is -20 m/s

Question :- 41

u= 20 m/s

v= 0m/s

a= 9.8 m/s²

$s = ut + \frac{1}{2} a {t}^{2}$

s = ?

u = 20m/s

a = 9.8 m/s²

t = 2s

s = (20)(2)+½(9.8)(2)²

s = 2×98×4

s = 784 m

Hence the height it will gain before begins to fall is 784m

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