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Practice Exercise¶

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: $Mv^2/2P$
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: $54J$
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: $6m$
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
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: $39.2J$
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: $3.5\times 10^9J$
The average power and instantaneous power become equal if work is done at
Any rate
Variable rate
Uniform rate
High rate
Ans: Uniform rate
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: $hp = 746 \text{watts}$
Proton, electron, neutron and $\alpha$ particles have same momentum. Which of them have highest K.E?
Proton
Electron
Neutron
$\alpha$ particle
Ans: Electron
The power output of a lamp is $6W$. How much energy does the lamp give out in $2$ minutes?
$3J$
$120J$
$720J$
$430J $
Ans: $720J$
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
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: $-mgg$
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
The tides raise the water in the sea roughly in a day
Once
Twice
Four time
Eight time
Ans: Twice
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
The highest value of escape velocity in solar system is for planet
Earth
Neptune
Jupiter
Moon
Ans: Jupiter
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
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: $4$
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
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: $-30J$
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: $3.6\times 10^{9}J$
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: $0$
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: $9 m/s$
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: $500J$
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: $v_{\text{esc}}=\sqrt{2}v_o$

Practice Exercise¶

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