## Chapter 4 – Turning Effect of Forces

**A force of 150 N can loosen a nut when applied at the end of a spanner 10cm long.**

F = 150 N

L = 10 cm = 0.1 m

So

t = F x L

t = 150 x 0.1

t = 15 Nm

** What should be the length of the spanner to loosen the same nut with a 60 N force?**

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**Ans:**As

t = F x L

15 = 60 x L

L = 15 / 60

L = 0.25 m

L = 25 cm

** How much force would be sufficient to loosen it with a 6 cm long spanner?**

**Ans: **As

L = 6 cm = 0.06 m

t = F x L

15 = F x 0.06 m

L = 15 / 0.06

L = 250 N

**Can a smart child play with a fat child on the see-saw? Explain how?**

**Ans: **Yes, Fat child can play with smart child by adjusting the moment arm.

**Two children are sitting on the see-saw, such that they can not swing. What is the net torque in this situation?**

**Ans: **In this case, net torque such that they can swing. In this case, net torque would be zero because clockwise torque is equal to Anticlockwise torque.

**A ladder leaning at a wall as shown in figure 4.31 is in equilibrium. How?**

**Ans: **Ladder is in equilibrium because it satisfies second condition of equilibrium.

**The weight of the ladder in figure 4.31 produces an anticlockwise torque. The wall pushes the ladder at its top end thus produces a clockwise torque. Does the ladder satisfy second condition for equilibrium?**

**Ans: **Yes, it satisfies second condition of equilibrium because both torques are equal in magnitude but opposite in direction.

**Does the speed of a ceiling fan go on increasing all the time?**

**Ans: **Speed of ceiling fan does not increase all the times. At acquiring maximum speed it moves with uniform speed. ** **

**Does the fan satisfy second condition for equilibrium when rotation with uniform speed?**

**Ans: **No, it does not satisfy the second condition of equilibrium. Because it neither in the state of rest nor moving with uniform velocity.

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