Question

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A stone is thrown horizontally from the top of the Cliff. It strikes the ground in 3 seconds at an angle of 45° with the horizontal. Determine the height of the tower and the speed of its projection?
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Answer 1

Explanation:

uy=0anday=g=9.8m/s2

sy=uyt+12ayt2

sy=0×3+12×9.8×(3)2

=44.1m

Thus, height of the tower is 44.1m.

Futher, vy=uy+ayt=0+(9.8)(3)=29.4m/s.

As the resultant velocity v makes an angle of 45∘ with the horizontal, so

tan45∘=vyvxor1=29.4vx

vx=29.4m/s

vx=ux+axt

⇒29.4=ux+0

or u_x = 29.4 m//s`

Therefore, the speed with which the body was projected (horizontally) is 29.4 m/s.

Answer 2

Answer:

Dimension of brick are =20cm×10cm×5cm

volume of 1 brick =20×10×5=1000cm

3

Dimension of wall =10m×15m×0.2m

volume of wall =10×15×0.2=30m

3

now no. of brick requried to make wall =

volumeof1brick

volumeofwall

no. of bricks =

1000m

3

30m

3

=

1000

30

×10

6

=30×10

3

[no. of bricks =30,000 bricks.]