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A ballon is rising up along the axis of a concave mirror of radius of curvature 20m . A ball is dropped from the ballon at a height 5m from the mirror when the ballon has velocity 20 m/s . The speed of the image of the ball formed by the concave mirror after 4 seconds is 20 n in m/s then n is – [take g=10m/s 2 ]

A ballon is rising up along the axis of a concave mirror of radius of curvature 20m . A ball is dropped from the ballon at a height 5m from the mirror when the ballon has velocity 20 m/s . The speed of the image of the ball formed by the concave mirror after 4 seconds is 20 n in m/s then n is –
[take g=10m/s2]

Grade:12

1 Answers

Vikas TU
14149 Points
6 years ago

We need to findthe last speed of inflatable after 4 sec and furthermore the last position of ball at 4 sec. At that point apply the newtons' first condition for speed count 
Given : u = 20 m/sec t= 4 sec and a = 10 m/s^2 
t=4 sec 
v=u+at 
V=20-10x4 = - 20 m/s 
s=ut +1/2 at2 
s=20x 4-1/2 x 10x 16=0m 
f(focal length) = Radius of shape/2 
= 10/2 = 5m 
Protest distance(u') = 15 m 
magnification=m=f/f-u' 
⇒-10/10-(- 15)=-2 
speed = magnification2 x Velocity of ball 
= - (- 2)²(- 20)=80m/s 
∴ANSWER=80m/s 
The estimation of n is 4 

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