Force and Pressure Test

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Force and Pressure Test - 35

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Question 1
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A force of $$500 N$$ acts on a square piece of plywood, each of whose sides is $$5 m$$ long. Calculate the pressure acting on the piece of plywood.

A
$$500 Nm^{-2}$$

B
$$100 Nm^{-2}$$

C
$$2500 Nm^{-2}$$

D
$$20 Nm^{-2}$$

Solution

The pressure is given as Force/Area.
In this case, the force is 500 N and area =$$5\times 5\quad =\quad 25{ m }^{ 2 }$$ as the side of the square plywood is given as 5 m.
Therefore, $$Pressure=\dfrac { Force }{ Area } =\dfrac { 500N }{ 25{ m }^{ 2 } } =20N/{ m }^{ 2 }$$.
Hence, the pressure acting on the piece of plywood is $$20N/{ m }^{ 2 }$$.
Question 2
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When a force acts on a large area, the pressure it exerts is more.

A
True

B
False

C
Ambiguous

D
Data insufficient

Solution

Answer is B.

The same force acting on a smaller area exerts a larger pressure, and a smaller pressure on a larger area. This is the reason why a nail has a pointed tip, knives have sharp edges and buildings have wide foundations.
For example, When standing, a person will sink more into sand than when he lies flat stretched on sand. The body weight acts on a smaller area, in standing position, than when the person lies stretched over a larger area.
Hence, the statement is false.
Question 3
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A force of $$400 N$$ exerts a pressure of $$20 N/cm^{2}$$. What is the area on which the force acts?

A
$$20m^{2}$$

B
$$20cm^{2}$$

C
$$1cm^{2}$$

D
$$10cm^{2}$$

Solution

The pressure is given as Force/Area.
In this case, the force is 400 N and the pressure exerted is $$20N/{ cm }^{ 2 }$$.
Therefore, $$Area=\dfrac { Force }{ Pressure } =\dfrac { 400N }{ 20N/{ cm }^{ 2 } } =20{ cm }^{ 2 }$$.
Hence, the area on which the force acts is $$20c{ m }^{ 2 }$$.
Question 4
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A boy stands on the ground. The area below his feet is $$70 cm^{2}$$. The pressure he exerts on the ground is $$7 N/cm^{2}$$. Calculate the total force acting on the ground.

A
$$0.1 N$$

B
$$10 N$$

C
$$490 N$$

D
$$4.9 N$$

Solution

The pressure is given as Force/Area.
In this case, the area =$$70{ cm }^{ 2 }$$and the presure acting is $$7N/{ cm }^{ 2 }$$.
Therefore, $$Force=Pressure\times Area\quad =\quad 7N/{ cm }^{ 2 }\times 70{ cm }^{ 2 }\quad =\quad 490N$$.
Hence, the total force acting on the ground is 490 N.
Question 5
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In the frozen northern regions of Canada, the Eskimos wear large snowshoes as that help them to walk on freshly fallen snow.

A
True

B
False

C
Ambiguous

D
Data insufficient

Solution

A snowshoe is a footwear for walking over the snow.

In the frozen regions of Canada, the freshly fallen snow is so soft, that it becomes difficult for a person to walk over it. Snowshoes work by distributing the weight of the person over a larger area so that the person's foot does not sink completely into the snow. Also, it increases the friction between the two surfaces. Hence, the Eskimos wear large snowshoes which help them to walk on freshly fallen snow.

Hence, the statement is true.
Question 6
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In a game of tug of war, three girls of team $$A$$ pull the rope with forces of $$100 N$$, $$120 N$$ and $$170 N$$. In team $$B$$, the three members pull the rope with forces of $$130 N$$, $$150 N$$ and $$155 N$$. Who will win the tug of war? What is the resultant force?

A
Team $$A$$, $$55 N$$

B
Team $$B$$, $$55 N$$

C
Team $$A$$, $$45 N$$

D
Team $$B$$, $$45 N$$

Solution

Resultant force is nothing but the total force acting on a body including their directions. If the object is at rest or it moves with a same velocity, the resultant force should be zero. All forces are acting on same direction, resultant force should be the sum of all the forces.

In this case, the forces applied by team A are 100 N, 120 N and 170 N. The total force is 100 N+120 N+170 N = 390 N. The forces applied by tema B are 130 N, 150 N and 155 N. The total force is 130 N+150 N+155 N=435 N.
Now, both the total forces are in the opposite direction as the team are in the opposite direction. So, the resultant force is 435 - 390 = 45 N.
Therefore, Team B will win in the game as they apply more force of 45 N.
Question 7
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A force exerts a pressure of $$45 N/m^{2}$$ when it acts on an area of $$10 m^{2}$$. Calculate the total force

A
$$4.5 N$$

B
$$450 N$$

C
$$45 N$$

D
$$.45 N$$

Solution

The pressure is given as Force/Area.
In this case, the area =$$10{ m }^{ 2 }$$and the presure acting is $$45N/{ m }^{ 2 }$$.
Therefore, $$Force=Pressure\times Area\quad =\quad 45N/{ m }^{ 2 }\times 10{ m }^{ 2 }\quad =\quad 450N$$.
Hence, the total force is 450 N.
Question 8
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Which of the pictures shows that a force changes the shape of an object?

A

B

C

D

Solution

In case-C, the given stuff is compressed by hand results decrease in diameter.so, that force changes the shape of an object.
Question 9
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Following diagram shows a moving tennis ball is hit by a player. What effect of the force is shown in the below picture ?

A
The force changes the direction of the moving object

B
The force changes the mass of the moving object

C
The force changes the shape of the moving object

D
The force can stop the moving object
Question 10
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You want to lift a heavy box. The force of gravity pulls it downwards with a force of $$500N$$. Your father applies an upward force of $$220 N$$ from below. How much force will you have to apply to lift it upwards?

A
$$720 N$$

B
$$280 N$$

C
$$180 N$$

D
$$380 N$$

Solution

The force of the gravitational pull is 500 N and the additional force of 220 N is applied in the opposite direction.
So, to lift the box, the box has to apply an extra force of 500 N - 220 N = 280 N in order to lift the box against the gravitational pull.
Resultant force is nothing but the total force acting on a body including their directions. Here, the gravitational force acts opposite to the force applied by the father and the boy.
Hence, the boy has to apply a force of 280 N to lift the box.