CHAPETR 9 FORCE AND LAWS OF MOTION
I VERY SHORT QUESTIONS ( 5 x 5=25)
1. A boy of mass 60 kg running at 3 m/s jumps on to a trolley of mass 140 kg moving with a velocity of 1.5 m/s in the same direction. What is their common velocity?
(m1=60kg,m2=140kg,u1=3m/s,u2=1.5m/s,v=?)
[Formula: m1u1+m2u2= (m1+m2)v]
Solution: (60×3) + (140×3) = (60+140)v
180 + 420 = 200v
600 = 200v
V= 3m/s
2. Obtain Expression for law conservation of momentum.
Solution: F1= m1(v1-u1)/t, F2=m2(v2-u2)/t, From Newton’s IIIrd law of motion
F1=-F2
m1(v1-u1)/t =- m2(v2-u2)/t
m1u1+m2u2=m1v1+m2v2
The total momentum of system remains constant.
3. A boy of mass 50 kg running at 6 m/s jumps on to a trolley of mass 150 kg moving with a velocity of 10 m/s in the same direction. What is their common velocity?
(m1=50kg,m2=150,u1=6m/s,u2=10m/s,v=?)
[Formula: m1u1+m2u2=(m1+m2)v]
Solution: (50×6) + (150×10) = (50+150)v
300 + 1500 = 200v
1800 = 200v
V= 9m/s
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