Online Test — Work and Energy
18 Questions • 15 min • Chapter MCQ
15:00
Question 1 of 18
Work is done by a force only when the object
is heavy
is displaced
feels a force but stays still
is hot
Explanation: Work needs a force and a displacement; with $s=0$, $W=Fs=0$.
Question 2 of 18
The formula for work done when force is along the displacement is
$W=Fs$
$W=\frac{F}{s}$
$W=mgh$
$W=\frac{1}{2}mv^2$
Explanation: $W=Fs$ for force along the displacement.
Question 3 of 18
A force of 20 N moves a body 5 m in its direction. The work done is
$4\,\text{J}$
$25\,\text{J}$
$100\,\text{J}$
$0\,\text{J}$
Explanation: $W=Fs=20\times5=100\,\text{J}$.
Question 4 of 18
The SI unit of work and energy is the
watt
newton
pascal
joule
Explanation: Both work and energy are measured in joules.
Question 5 of 18
Work done by friction on a moving body is
positive
negative
zero
very large positive
Explanation: Friction opposes motion, so it does negative work.
Question 6 of 18
A man pushes a wall but it does not move. The work done is
large
zero
negative
1 J
Explanation: No displacement means $W=Fs=0$.
Question 7 of 18
The kinetic energy of a body of mass $m$ moving with speed $v$ is
$mv$
$\frac{1}{2}mv^2$
$mgh$
$mv^2$
Explanation: $E_k=\frac{1}{2}mv^2$.
Question 8 of 18
The kinetic energy of a 4 kg body moving at 3 m/s is
$12\,\text{J}$
$18\,\text{J}$
$36\,\text{J}$
$6\,\text{J}$
Explanation: $E_k=\frac{1}{2}\times4\times3^2=18\,\text{J}$.
Question 9 of 18
If the speed of a body is doubled, its kinetic energy becomes
double
half
four times
the same
Explanation: $E_k\propto v^2$, so doubling $v$ gives four times the energy.
Question 10 of 18
Gravitational potential energy of a body at height $h$ is
$mgh$
$\frac{1}{2}mv^2$
$Fs$
$\frac{W}{t}$
Explanation: $E_p=mgh$.
Question 11 of 18
The potential energy of a 5 kg body at 4 m height ($g=10\,\text{m/s}^2$) is
$20\,\text{J}$
$200\,\text{J}$
$50\,\text{J}$
$2\,\text{J}$
Explanation: $E_p=mgh=5\times10\times4=200\,\text{J}$.
Question 12 of 18
The work-energy theorem states that work done by the net force equals the change in
potential energy
kinetic energy
mass
power
Explanation: $W=\Delta E_k$.
Question 13 of 18
Energy can neither be created nor destroyed. This is the law of
gravitation
conservation of energy
inertia
motion
Explanation: It is the law of conservation of energy.
Question 14 of 18
At the top of its fall, a freely dropped ball has
maximum KE, zero PE
maximum PE, zero KE
zero PE and zero KE
equal PE and KE
Explanation: At the top it is at rest, so all energy is potential, $E_p=mgh$.
Question 15 of 18
Power is defined as
$Fs$
$mgh$
$\frac{W}{t}$
$\frac{1}{2}mv^2$
Explanation: Power $P=\frac{W}{t}$, the rate of doing work.
Question 16 of 18
The SI unit of power is the
joule
newton
kWh
watt
Explanation: $1\,\text{W}=1\,\text{J/s}$.
Question 17 of 18
A machine does 900 J of work in 3 s. Its power is
$300\,\text{W}$
$2700\,\text{W}$
$3\,\text{W}$
$30\,\text{W}$
Explanation: $P=\frac{900}{3}=300\,\text{W}$.
Question 18 of 18
One kilowatt-hour ($1\,\text{kWh}$) equals
$3600\,\text{J}$
$1000\,\text{J}$
$3.6\times10^6\,\text{J}$
$36\,\text{J}$
Explanation: $1\,\text{kWh}=1000\,\text{W}\times3600\,\text{s}=3.6\times10^6\,\text{J}$.