2 Marks Questions

Question 12 Marks

A woman throws an object of mass 500 g with a speed of $25 \mathrm{~m} \mathrm{~s}^1$.
What is the impulse imparted to the object?

Answer

Mass of object m = 500 g = 0.5kg u = 0, v = 25m/ s Impulse $\vec{\text{F}}.\text{dt}=\frac{\text{d}\vec{\text{p}}}{\text{dt}}=\text{d}\vec{\text{p}}=\text{m}\vec{\text{v}}-\text{m}\vec{\text{u}}$$\text{I}=\Delta\vec{\text{p}}=\text{m}(\vec{\text{v}}-\vec{\text{u}})=0.5(25.5)\text{N}-\text{s}$

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Question 22 Marks

A person of mass 50 kg stands on a weighing scale on a lift. If the lift is descending with a downward acceleration of $9 \mathrm{~m} \mathrm{~s}{ }^{-2}$, what would be the reading of the weighing scale? $\left(\mathrm{g}=10 \mathrm{~m} \mathrm{~s}^{-2}\right)$

Answer

When lift is descending with acceleration a, the apparent weight decreases on weighing scale$\therefore\text{W}'=\text{R}=(\text{mg}-\text{ma})=\text{m}(\text{g}-\text{a})$
Apparent weight due to reaction force by the lift on weighing scale.$\therefore\text{W}'=50(10-9)=50\text{N}$
Reading of weighing scale $=\frac{\text{R}}{\text{g}}=\frac{50}{10}=5\text{kg}$

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Question 32 Marks

A block of mass M is held against a rough vertical wall by pressing it with a finger. If the coefficient of friction between the block and the wall is $\mu$ and the acceleration due to gravity is g, calculate the minimum force required to be applied by the finger to hold the block against the wall?

Answer

Let F force is applied by the finger on a body of mass M to hold rest against the wall. Under the balanced condition

$\text{F}=\text{N} $ and $\text{f}=\text{Mg}$
$\Rightarrow\mu\text{F}=\text{Mg}$ or $\text{F}=\frac{\text{Mg}}{\mu}$ is the minimum force to hold the block against the wall at rest.

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Question 42 Marks

A person driving a car suddenly applies the brakes on seeing a child on the road ahead. If he is not wearing seat belt, he falls forward and hits his head against the steering wheel. Why?

Answer

When a person applies breaks suddenly, the lower part of person slows rapidly with the car, but the upper part of driver continue to move with same speed in the same direction due to the inertia of motion and his head car hit with steering.

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Question 52 Marks

A mass of 2kg is suspended with thread AB Thread CD of the same type is attached to the other end of 2kg mass. Lower thread is pulled gradually, harder and harder in the downward directon so as to apply force on AB. Which of the threads will break and why?

Answer

Thread AB will break. Force on CD is equal to the force (f) applied at D downward, but the force on thread AB is equal to the force F along with force due to mass 2kg downward. so the force on AB is 2kg more than applied force at D.Hence the thread AB will break up.

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Question 62 Marks

Block A of weight 100N rests on a frictionless inclined plane of slope angle 30° A flexible cord attached to A passes over a frictonless pulley and is connected to block B of weight W. Find the weight W for which the system is in equilibrium.

Answer

Main concept used: On balanced condition i.e., no motion then no frictional force or f = 0 Explanation: During equilibrium of A or B$\text{mg}\sin30^\circ=\text{f}$
$\frac{1}{2}\text{mg}=\text{F}\ [\because\text{mg}=100\ \text{N}]$
$\therefore\text{F}=\frac{1}{2}\times100=100=50$
For B is at rest W = F =50N.

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Physics 2 Marks Questions

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