Last update: 6 years ago by nmanumr

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Practice Exercise

1. A car of mass $m$ has an engine which can deliver power $P$, what is the minimum time in which the car can be accelerated from rest to speed

   $Mv/P$

   $P/Mv$

   $Mv^2/2P$

   $P/Mv^2$
   Ans: $Mv^2/2P$

2. Under the influence of a force, an object of mass $4kg$ accelerates from $3 m/s$ to $6 m/s$ in $8s$. How much work was done on the object during this time?

   $27J$

   $54J$

   $72J$

   $96J$
   Ans: $54J$

3. A $500gm$ ball is thrown vertically upward with K.E of $58.8J$ the K.E is reduced to half at a height of _____m above point of projections

   $2m$

   $3m$

   $5m$

   $6m$
   Ans: $6m$

4. Which of the following types of force does no work on the particle when it acts on it?

   Frictional force

   Gravitational force

   Elastic force

   Centripetal Force
   Ans: Centripetal Force

5. If a body of mass of $2kg$ is raised vertically through $2m$, then the work done will be

   $38.2J$

   $392.1J$

   $39.2J$

   $3.92J$
   Ans: $39.2J$

6. An elevator weighing $3.5\times 10^{6}N$ is raised to a height of $1000m$ in the absence of friction, the work done is

   $3.5\times 10^3J$

   $3.5\times 10^4J$

   $3.5\times 10^6J$

   $3.5\times 10^9J$
   Ans: $3.5\times 10^9J$

7. The average power and instantaneous power become equal if work is done at

   Any rate

   Variable rate

   Uniform rate

   High rate
   Ans: Uniform rate

8. The relation between horse power and watt is

   $1hp = 546 \text{watts}$

   $hp = 746 \text{watts}$

   $1hp = 1000 \text{watts}$

   $1hp = 946 \text{watts}$
   Ans: $hp = 746 \text{watts}$

9. Proton, electron, neutron and $\alpha$ particles have same momentum. Which of them have highest K.E?

   Proton

   Electron

   Neutron

   $\alpha$ particle
   Ans: Electron

10. The power output of a lamp is $6W$. How much energy does the lamp give out in $2$ minutes?

    $3J$

    $120J$

    $720J$

    $430J $
    Ans: $720J$

11. Work done by variable force is determine by dividing

    Force into small interval

    Displacement into small interval

    Both force and displacement into small intervals

    Force into small and displacement into large intervals
    Ans: Displacement into small interval

12. A box of mass $m$ slides down a frictionless inclined plane of length $L$ and vertical height $h$. What is the change in its gravitational potential energy

    $-mgL$

    $-mgg$

    $-mgL/h$

    $-mgh/L$
    Ans: $-mgg$

13. The escape velocity of a body in gravitational field of earth independent of

    Its mass

    The angle at which it is thrown

    Both its mass and the angle at which it is thrown

    Gravitational field of earth
    Ans: Both its mass and the angle at which it is thrown

14. The tides raise the water in the sea roughly in a day

    Once

    Twice

    Four time

    Eight time
    Ans: Twice

15. The source of geothermal energy is

    Decay of radioactive clement in the earth

    Compression of material in the earth

    Residual heat of the earth

    All in a, b and c
    Ans: All in a, b and c

16. The highest value of escape velocity in solar system is for planet

    Earth

    Neptune

    Jupiter

    Moon
    Ans: Jupiter

17. Work done by the force of friction is

    Always positive

    Always negative

    Positive only for small frictional force

    Positive only for large frictional force
    Ans: Always negative

18. A body of mass $2 kg$ is projected vertically upwards with a velocity of $2 m/s$. The kinetic energy of the body just before striking the ground is

    $2$

    $4$

    $6$

    $8$
    Ans: $4$

19. If velocity is doubled, then

    Momentum increases to 4 times and KE increases to 2 times

    Momentum and KE remain same

    Momentum increases to 2 times and KE increases constant

    Momentum increases to 2 times and KE increases to 4 times
    Ans: Momentum increases to 2 times and KE increases to 4 times

20. While a person lifts a book of mass $2 kg$ from the floor to a tabletop, $1.5 m$ above the floor, how much work does the gravitational force do on the book?

    $-30J$

    $0J$

    $-10J$

    $-I5J$
    Ans: $-30J$

21. One mega watt hour is equal to

    $3.6\times 10^{6}J$

    $3.6\times 10^{12}J$

    $3.6\times 10^{8}J$

    $3.6\times 10^{9}J$
    Ans: $3.6\times 10^{9}J$

22. A boy holds a $40N$ weight at arm's length for $10s$. His arm is $1.5m$ above the ground. The work done by the force of the boy on the weight while he is holding it is:

    $0$

    $90J$

    $60J$

    $40J$
    Ans: $0$

23. A block of mass $3kg$ slides down a frictionless inclined plane of length $6m$ and height $4m$. If the block is released from rest at the top of the incline, what is its speed at the bottom?

    $5 m/s$

    $8 m/s$

    $6 m/s$

    $9 m/s$
    Ans: $9 m/s$

24. A man pulls a $100N$ crate up a frictionless $30^o$ slope $5m$ high, as shown. Assuming that the crate moves at constant speed, the work done by the man is

    $-5000J$

    $500J$

    $-250J$

    $0J$
    Ans: $500J$

25. The relation between the escape velocity $v_{\text{esc}}$ and orbital speed $v_o$ is given by

    $v_{\text{esc}}=\frac{1}{2}v_o$

    $v_{\text{esc}}=\sqrt{2}v_o$

    $v_{\text{esc}}=v_o$

    $v_{\text{esc}}=2v_o$
    Ans: $v_{\text{esc}}=\sqrt{2}v_o$

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