9th Class
Science
Force and laws of motion
Question Bank
Force and Laws of Motion
question_answer
A dish of mass 10 gm is kept horizontally in air by firing bullets of mass 5 g each at the rate of 10 per sec. If the bullets rebound with the same speed, what is the velocity with which the bullets are fired?
A) 49 cm/sec
B) 147 cm/sec
C) 98 cm/sec
D) 196 cm/sec
Correct Answer:
C
Solution :
Weight of the dish\[=\frac{10}{1000}\times g\] Speed of the bullet \[=v\] Rate of change of momentum of bullets \[=\frac{2\times 10\times 5}{1000}v\]\[=\]applied force on the dish Now,\[\frac{2\times 10\times 5}{1000}v=\frac{10\times g}{1000}\] \[\therefore \] \[v=0.98\,\,m/s=98\,\,cm/s\]