Questions and Answers - Second Law of Motion

? If F = 61-8j+10k reduces acceleration of Im/s2 in a body calculate the mass of the body? ans: F=(6i-8j+10k) a)10 kg m 1a'l b) 1052 kg = () V2 10 kg 62+(--2)+102 m = 1052 I = 36+64+100 d)20 kg = 1052 kg = 200 =V 2x100 = 2 x10 = 1052

? A bullet of mass 5g moving with a velocity 100m/c penetraits the wooden ( lock upto 6cm. The average force imported by the bullet on the block is? ans: F=ma 100mls V=0 n=5g 5x10 kg Buller 6cm S=5cm V2 =u'tras = 6x10mm 10 HOT 02=100 = 2xax 6x102 " , = -100-=2ax 6x102 F= 52103-1 = 10 =a 12 12x102 = 0.417x103 a -106 12 = -417N

? A cliwali rocket is ejecting 0.05kg of gases /s at a velocity of 400m/s the accelerating force of arocket is ? ans: am = 0.05kg/s at V= 400mls F = Vx am at = 400x0.05 = 20W ? A body of mass 2kg moving on a horizontal surface with an initial velocity of unis comes

to rest after 2 seconds. if one wants to keep this body moving on the same surface with a velocity of umis.The force required is? a= V-u u=4mls ans : t V=O t = 2 Sec # a= 0-4 = - 2m/s' 2 F= 2 x - 2 =-6N - -4N 4N

? ves An object with a mass 10kg most at a const- ant velocity of lom/s . A constant force then acts for 4 second on the object and gives it a co- nstant speed 2mls in the opposite direction. of Find the force acting on the objet? ans: mass = 2kg V=-2 4=10 t 45ec F=ma V-ce = (-2)-10 -12 = -3 =10x-3 t 4 4 = -30N eighing ? A block of metal waiting 2 kg is resting on a fric tionless plane. it is struck by age r- cleasing watch at a rate Of I kg /second and at aspeed of 3mls The initial acc eleration Of the block is ? Force = I kgwt ans: F= V X am = 1x9.8 at \ kgwt = 9.3N2 10N = 5x1 F= BN a= F/m = 5/2 = 2.9m/s2 w=mg

? in a rocket of mass 1000 kg fuel is consumed at a rate of 40 kg/s. The velocity of the gases Force ejected from the rocket is 5x10 mis. The trust on the rocket is ? ans: m=1000kg V= 5x10 m ls vam at 5x10 x 1000 40 = 20 2x10°N ? At a place where g is 10m/s2. Force of 5 kgwt weight acts on a body of mass 10kg initially at rest. The velocity of the body after 4 seconds is? ans: g = 10m/s u=o F. 5 kgwt = 50N (10xs) utat =V m= 10 kg 0 + 5x6 = 20m/s a = F = 30/10 = 5m/s2 m 1 a): Find displacement after 5 seconds? S= at +1/2at2 = 1/2x5x52 = 1/2x9x25 = 62.5m