20Class Exercise - 1Two masses of 1 g and 4 g are moving with KE in the ratio of 4 : 1. The ratio of their linear momentum is1 : 1 (b) 1 : 2(c) 4 : 1 (d) 16 : 1
21SolutionWe know that if P is the linear momentum of the particle, thenHence answer is (a)
22Class Exercise - 2A bullet hits a block kept at rest on a smooth horizontal surface and gets embedded into it. Which of the following does not change?(a) Linear momentum of the block(b) PE of the block(c) KE of the block(d) Temperature of the block
23SolutionSince in the absence of external forces on the system (bullet + block) linear momentum of system does not change. But since external force acted on the block during collision, the block changes its momentum. KE is also not conserved as some amount of heat energy is lost when bullet penetrated into the block. Temperature also increases during the process.Hence answer is (b)
24Consider the following two statements. Class Exercise - 3Consider the following two statements.The linear momentum is independentof frame of reference.II. The kinetic energy is independent offrame of reference.Both I and II are true (b) Both I and II are false(c) II is true but I is false (d) I is true but II is false
25SolutionVelocity of any body is dependent upon the choice of frame of reference. For example, a man sitting in train finds his co-passenger at rest and hence, having neither momentum nor kinetic energy. But the same man has both momentum and kinetic energy with respect to a man standing on a bus-stand.Hence answer is (b)
26Class Exercise - 4A nucleus of mass number A originally at rest, emits an - particle with speed v. The recoil speed of daughter nucleus is equal to
27Solution u = 0 Before emission: A V’ v After emission a 4 A - 4 Since there are no external forces acting on the system, hencePf = PiÞ A(u) = (A – 4)v´ + 4vÞ A(0) = (A – 4)v´ + 4v
28Class Exercise - 5A shell is fired from a cannon with a velocity v making an angle with the horizontal. At the highest point in its path it explodes into two pieces of equal masses. One of the particle retraces its path to the cannon. What is the speed of the other piece?
29Solution At the highest point velocity has only horizontal component. Since there are no external forces acting in horizontal direction, momentum is conserved.\ Pf = PixyÞ v´ = 3v cosq
30Class Exercise - 6A 150 g cricket ball, bowled at a speed of 40 m/s is hit straight back to the bowler at a speed of 60 m/s. What is the magnitude of the average force on the ball from the bat if the bat is in contact with the ball for 5.0 ms?
32(a) What impulse acts on the ball during the contact? Class Exercise - 7A 2 kg ball drops vertically onto a floor, hitting with a speed of 25 m/s. It rebounds with an initial speed of 10 m/s.(a) What impulse acts on the ball during the contact?(b) If the ball is in contact with the floor for s, what is the magnitude of the average force on the floor from the ball?
33Solution m = 2 kg vi = 25 m/s vf = 10 m/s Change in momentum DP = m(vf – vi)= 2( )= 70(a) \ Impulse = +70 N-s(b) Now, impulse = F· tÞ 70 N-S = F × (0.020)\ Force on the floor from the ball = 3500 N
34Class Exercise - 8Figure above shows an approximate plot of force magnitude versus time during the collision of 100 g ball with a wall. The initial velocity of the ball is 50 m/s and it rebounds directly back withapproximately the same speed perpendicular to the wall as was in the case of impact. What is Fmax, the maximum magnitude of the force on the ball from the wall during the collision?246ForceForce (N)Time
36Class Exercise - 9A 2100 kg truck traveling north at 50 m/s turns east and accelerates to 60 m/s.(i) What is the change in kinetic energy of the truck?(ii) What is the change in linear momentum of the truck?