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# Tag Archives: mechanics

## What is torsion?

What is torsion?

Torsion means the twisting of an object due a torque applied on it.

Also defined as the deformation caused when one end of an object is twisted in one direction and the other end is held motionless or twisted in the opposite direction.

## What is resultant force?

“What is resultant force?”

When a number of frces are acting simultaneously on a body, it will be producing an effect – may be keeping the body in equilibrium, or giving it an acceleration in a particular direction.

Resultant of a number of forces is defined as that single force which can replace all other forces to produce the same effect.

If the number of forces acting on the body keep it at rest or maintain uniform motion,it is said to  be in equilibrium; then the resultant is zero (since acceleration is zero).

## Numericals from Kinematics

Posted By – Abdul Hameed

1. During the first 18 minutes of a 1.0-hour trip, a car has an average speed of 11 m/s. What must the average speed of the car be during the last 42 minutes of the trip be if the car is to have an average speed of 21 m/s for the entire trip?
2. An elevator is moving upward with a speed of 11 m/s. Three seconds later, the elevator is still moving upward, but its speed has been reduced to 5.0 m/s. What is the average acceleration of the elevator during the 3.0 s interval?
3. A turtle takes 3.5 minutes to walk 18 m toward the south along a deserted highway. A truck driver stops and picks up the turtle. The driver takes the turtle to a town 1.1 km to the north with an average speed of 12 m/s. What is the magnitude of the average velocity of the turtle for its entire journey?

## A numerical from Projectile motion, friction and more

One side of the roof of a building slopes up at 33.5°. A roofer kicks a round, flat rock that has been thrown onto the roof by a neighborhood child. The rock slides straight up the incline with an initial speed of 15.0 m/s. The coefficient of kinetic friction between the rock and the roof is 0.430. The rock slides 10.0 m up the roof to its peak. It crosses the ridge and goes into free fall, following a parabolic trajectory above the far side of the roof, with negligible air resistance. Determine the maximum height the rock reaches above the point where it was kicked.

(The question is left for visitors to answer.)

## An Idea for Cycle Rickshaw

Sir,
While seeing a rickshaw puller struggling to pull heavy weight,I wondered if the load carried by him can be reduced for carrying same weight people.Since the load carried by him is dependent on the horizontal component of frictional force (i.e,µ.mgsinØ) ,cant we apply a spring in the rickshaw so that the effective weight will decrease and hence the load carried by him?

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