CBSE PHYSICS : Challenging Questions
1. A machine gun can fire bullet of 50gm at speed of 2000m/s ,the man holding the gun can exert an average force of 200N against the gun . Calculate the maximum number of bullet which he can fire per minute ( Ans: 120 )2. A machine gun can fire 20 bullet per second ,if the speed of the bullet is 100m/s and if each bullet is of weight 100gms , then calculate force require to hold the gun in its position. ( Ans: 200N )
3. A man in a circus show jumps from a height of 10m and is caught by a net spread below him. The net sags below by 2m . Find the force exerted by the net on the man to stop him. Mass is 60kg and acceleration is 10m/s2. (Ans: 300N)
4. A machine gun is fitted on a trolley of mass 2000kg on a horizontal frictionless surface. If the gun fires bullet each of mass 10gm with a velocity of 500m/s with respect to the trolly and if the number of bullet fired per second is 10 then calculate the average thrust exerted by ejected bullet on the system (Ans: 50N)
5. Two identical blocks A and B each of mass M are connected to each other through a light string. The system is placed on a smooth horizontal floor. When constant force F is applied horizontally on the block A, find the tension in the string. (Ans: F/2)
6. A hunter fires 50 g bullets from a machine gun. If each bullet moves with a velocity of 150ms−1 how many such bullets are to be fired into a tiger of mass 60 kg coming towards him with a velocity of 10ms−1 in order to stop the tiger? (Ans: 80)
7. A machine gun fires 240 bullets per minute with a velocity of 500m/s . If the mass of each of the bullet is 5×10−2 kg , find the power of the gun.( Ans: 2500W)
8. The momentum of a body is double. By what percentage does its kinetic energy increase?
(Ans: 300%)
(Ans: 300%)
9. A machine gun is mounted on a flat rail road car. The gun is firing bullets at the rate of 10 bullets per second each of mass 10 g. The bullets come out with velocity 500 m/s relative to the car. Calculate the acceleration of the car at the instant when its mass is 200 kg. Also calculate the force at the instant. (Ans: F = 50N)
10. A machine gun fires 240 bullets per minute with certain velocity . If the mass of each bullets 10-2 kg and the power of the gun is 7.2 k.W, find the velocity which each bullet is fire. (Ans: 600 m/s)
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ReplyDeleteQ. A hunter fires 50 g bullets from a machine gun. If each bullet moves with a velocity of 150ms−1 how many such bullets are to be fired into a tiger of mass 60 kg coming towards him with a velocity of 10ms−1 in order to stop the tiger?
ReplyDeleteSolution: Let n be the number of bullets each of mass m fired with a velocity v towards a tiger of mass M moving with a velocity V. When the tiger stops, applying the principle of conservation of linear momentum
n (mv) +MV = 0 (Final momentum = 0)
n = −[ MV]/[ mv]
Hence m = 50 g = 50×10−3 kg ; v = 150ms−1 , M = 60 kg , V =-10ms−1
n = -[60 x -10] [50x10-3x150] = 80
Q. A machine gun fires 240 bullets per minute with a velocity of 500ms−1 . If the mass of each of the bullet is 5×10−2 kg , find the power of the gun.
Solution: The power of the gun = n{KE}/t where n is the number of bullets fired by the gun in a time interval t, m is the mass of the bullet and v is its velocity.
Here, n = 240 , t = 1 minute =60s ; m = 50×10-2 kg; v=500ms-1.
The power of the gun = n{KE}/t = [240 x ½ x50×10-2x(500)2] 60 = 2500W
Q. State two applications of impulse.
Solution: 1.Shock absorbers are used in vehicles to reduce the magnitude of impulsive force when they travel on uneven roads.
2. While catching a ball, a cricket player lowers his hands to reduce the impulsive force and save himself from getting hurt