Question

7.
A particle starts moving from position of rest under a constant acceleration. If it travels a distance x int
sec. The distance it will travel in next t sec will be
(A)2x
(B) 3x
(C) 4x
(D) 5x

Answer 1

Answer:

A particle starts from the position of rest under a constant acceleration. It travels a distance x in the first 10 seconds and distance y in the next 20 seconds. Then

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ANSWER

initially velocity is zero, and acceleration is a, so distance covered in 10 sec is x=

2

1

a10

2

=50a

now distance covered in total 30 sec is x+y=

2

1

a30

2

=450a

so y=400a,x=50a

so y=8x

best option is option A

Answer 2

Explanation:

The energy of one photon is

E=

λ

hc

=

0.57×10

−6

6.626×10

−34

Js×3×10

8

m/s

=3.487×10

−19

J .

25 watt corresponds to 25 J per second.

The number of photons emitted per second is

3.487×10

−19

25

=7.17×10

19

/s.