Question

A disc of mass 100 g is kept floating horizontally in air by firing bullets, each of mass 5 g with the same velocity at the
same rate of 10 bullets per second. The bullets rebound with the same speed in opposite direction, the velocity of each
bullet at the time of impact is:
196 cm/s
9.8 cm/s
98 cm/s
980 cm/s​

Answer 1

Answer:

Suppose speed of firing is V then after

rebounding the momentum frees fessed

to the dis will be charge in momentum

ΔP=−mv−(mv)=−2mv

↑

initial

Value =∣ΔP∣=2mv

⇒ Fr 10 bullets 10×2=20mv

m=0.05kg⇒∣ΔP∣

total

=v

time Δt=1 second

⇒ Fore entered =

Δt

∣ΔP∣

total

=

1

v

=v Newton

it should balance the eight of disc

to prevent it from falling

So =Mg=1×9.8

⇒v=9.8mls

Answer 2

↑

initial

Value =∣ΔP∣=2mv

⇒ Fr 10 bullets 10×2=20mv

m=0.05kg⇒∣ΔP∣

total

=v

time Δt=1 second

⇒ Fore entered =

Δt

∣ΔP∣

total

=

1

v

=v Newton

it should balance the eight of disc

to prevent it from falling

So =Mg=1×9.8

⇒v=9.8mls