From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 m s-1. Calculate the initial recoil velocity of the rifle.
Mass of the rifle, m1 = 4 kg
Mass of the bullet, m2 = 50g = 0.05 kg
Recoil velocity of the rifle = v1
Bullet is fired with an initial velocity, v2 = 35 m/s
Total mass = m1 + m2 = 4 + 0.05 = 4.05 kg
Since the system was at rest , velocity (v) = 0
Momentum ( before firing ) = mass x velocity = ( m1 + m2 )v = ( 4.05 ) 0 = 0 kg m/s
Total momentum = momentum of bullet + momentum of rifle = m1 v1 + m2 v2
= 0.05 x 35 + 4 x v2 = 7/4 + 4 v2
Since the total momentum remain conserved
Total momentum before firing = Total momentum after firing
0 = 7/4 + 4 v2
4 v2 = - 7/4
v2 = - 7/16
v2 = -04375 m/s
Thus , the recoil velocity of the pistol is -0.4375 m/s .
The negative sign of velocity means that the rifle will recoil in the opposite direction of the bullet.
Abdul, while driving to school, computes the average speed for his trip to be 20 km h-1. On his return trip along the same route, there is less traffic and the average speed is 40 km h-1. What is the average speed for Abdul’s trip?
An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.
A driver of a car travelling at 52 km h-1 applies the brakes and accelerates uniformly in the opposite direction. The car stops in 5 s. Another driver going at 3 km h-1 in another car applies his brakes slowly and stops in 10 s. On the same graph paper, plot the speed versus time graphs for the two cars. Which of the two cars travelled farther after the brakes were applied?
Fig 8.11 shows the distance-time graph of three objects A,B and C. Study the graph and answer the following questions:
Fig. 8.11
(a) Which of the three is travelling the fastest?
(b) Are all three ever at the same point on the road?
(c) How far has C travelled when B passes A?
(d) How far has B travelled by the time it passes C?
Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is 2.5 m s-1 before the collision during which they stick together. What will be the velocity of the combined object after collision?
Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?
Two objects of masses 100 g and 200 g are moving along the same line and direction with velocities of 2 m s-1 and 1 m s-1, respectively. They collide and after the collision, the first object moves at a velocity of 1.67 m s-1. Determine the velocity of the second object.
How do poriferan animals differ from coelenterate animals?
The speed-time graph for a car is shown is Fig. 8.12.
Fig. 8.12
(a) Find how far does the car travel in the first 4 seconds. Shade the area on the graph that represents the distance travelled by the car during the period.
(b) Which part of the graph represents uniform motion of the car?
How are sol, solution and suspension different from each other?
What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?
A lamp consumes 1000 J of electrical energy in 10 s. What is its power?
An object of mass, m is moving with a constant velocity, v. How much work should be done on the object in order to bring the object to rest?
If number of electrons in an atom is 8 and number of protons is also 8, then (i) what is the atomic number of the atom? and (ii) what is the charge on the atom?
Explain how the human ear works.
What is power?
Name two biologically important compounds that contain both oxygen and nitrogen.
When a carpet is beaten with a stick, dust comes out of it. Explain.
Why is water essential for life?
Explain the following giving examples.
(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension