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## DECREASING PRESSURE BY INCREASING AREA

The pressure exerted by a given force can be decreased by increasing the area of contact.

# P=F/A

The equation shows that pressure is inversely proportional to area.

## FOUNDATION OF BUILDINGS

The foundation off building is made more broader than the rest of the building so that the pressure exerted by the weight on earth can be decreased.

## SHOULDER STRAPS OF SCHOOL BAGS

The shoulder straps of school bags are made wider and soft so that the pressure exerted by the heavy bags on shoulders can be reduced. You can feel the paining pressure if you try to replace the broad strap with a narrow one.

FEET OF ELEPHANT AND CAMEL

## MILITARY TANK

The Military tanks have a broad chain so that the pressure exerted by the heavy vehicle on ground is a minimum and it can travel even through marshy places

• Heavy Vehicles have more tyres
• When vehicles get struck in marshy places, wooden planks are used for the vehicle to come up.

## An interesting numerical problem from kinematics

George’s favorite food was bananas. One day he was walking with his friend, the man in the yellow hat, as he was eating a banana. They were in New York City and they were walking up the Empire State Building. Finally they made it to the top! George spied a nice young woman walking down 5th avenue balancing this hat on her head.  She was very noticeable for she was six feet tall! George, being the troublemaker he was, wanted to see if he could drop his banana peel in her hat. He noticed that she was jogging at a constant pace of 6 miles per hour. George was on the 102nd floor observatory, which is 1,224 feet from the ground.*
Assuming that George lands the banana peel in the hat……..
A)      How long will the banana peel be in the air? (Assuming there is no wind and the banana will drop straight down from the empire state building)
B)      What will the velocity of the banana peel be right before it lands in the woman’s hat?
C)      How far away must the woman’s hat be from the landing point of the banana peel (horizontally) when George makes his scandalous move and drops the peel.
D)      If George decides to throw another peel one second later to land it on the ground and trip the jogger, at what velocity must he throw it at so that it hits the ground at the same the original peel lands in the hat.

## Numerical Problems from Kinematics and Force

1.if a man in a boat rows perpendicular to the bank he is drifted 120 m during crossing river in 10 minutes . if he heads at angle of alpha from upstream he crosses river by shortest path in 12.5 min.
find width of river,velocity of river with respect to water,velocity of boat with respect to river

2.a projectile is thrown horizontally from top of building of height 10 m with a certain speed u.at same time another projectile thrown from ground 10 m away from building with equal speed u in same vertical plane at angle theta with horizontal.if they collide after 1 second then find u and angle of projections of 1st and 2nd particle

3.a 10 kg block is resting on a rough surface .when force is applied to it for 4s. the variation of force with time is given as (f=100N for 4s.). also (coefficient of friction=0.5) find velocity at t=1s and t=4s.

4. a particle moves in straight line whose acceleration depends on velocity as a=-alpha root v, alpha =+ve constant . at initial moment velocity of particle is Vo.if average speed before it stops is Vo/x find value of x.

## 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.)

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