Q 1 :

An elastic spring under tension of 3 N has a length a. Its length is b under tension 2 N. For its length (3a-2b), the value of tension will be ______ N.             [2024]



(5)     k(a-x0)=3⇒a=3k+x0                ...(i)

          k(b-x0)=2⇒b=2k+x0               ...(ii)

          Now, 3a-2b=9k+3x0-4k-2x0=5k+x0

          ⇒{(3a-2b)-x0}=5k

           ⇒k{(3a-2b)-x0}=5     ∴T=5N

 



Q 2 :

A massless spring gets elongated by amount x1 under a tension of 5 N. Its elongation is x2 under the tension of 7 N. For the elongation of (5x1–2x2), the tension in the spring will be,         [2025]

  • 15 N

     

  • 20 N

     

  • 11 N

     

  • 39 N

     

(3)

kx1=5 N ⇒ x1=5k

kx2=7 N ⇒ x2=7k

Then (5x1–2x2)k=5×5–2×7=11 N.



Q 3 :

The length of a light string is 1.4 m when the tension on it is 5 N. If the tension increases to 7 N. the length of the string is 1.56 m. The original length of the string is ______ m.          [2025]



(1)

T=K(l–l0)

⇒ 5=K(1.4–l0)

⇒ 7=K(1.56–l0)

⇒ 51.4–l0=71.56–l0

∴ l0=1 m



Q 4 :

Find the ratio of the extension in upper spring to lower spring.

  • m1k1m2k2

     

  • m2k1m1k2

     

  • (m1+m2)k2m1k1

     

  • (m1+m2)k2m2k1

     

(4)

k1x1=k2x2+m1g;    k2x2=m2g

x1=k2k1[m2gk2]+m1gk1

x2=m2gk2

x1=(m1+m2)gk1

x1x2=(m1+m2)k2k1m2