97 past paper MCQs from Physics unit 3, Work and Energy, across 6 topics. They are arranged topic by topic; bigger topics show a sample here and link to their full set and to study notes. Tap “Show answer” for the correct option and a short solution.
1.A 10 N force moves a body around a circular path of radius 50 cm. What is the work done in completing one revolution? (MDCAT 2020)
Correct answer: (b) zero
The body returns to its starting point, so the displacement is zero and so is the work.
2.The area under a force-displacement graph gives us the: (MDCAT 2020)
Correct answer: (c) work
Force multiplied by displacement is work, and that product is the area under the graph.
3.The work done by a variable force can be found by dividing the: (MDCAT 2023)
Correct answer: (b) displacement into small intervals
Over a small enough displacement the force is effectively constant, so $W=\sum F\Delta d$ is the area under the force-displacement graph.
All 24 Work MCQs → Work notes →
4.A particle of mass $m$ at rest is acted upon by a force $P$ for a time $t$. Its kinetic energy after time $t$ is: (MDCAT 2022)
Correct answer: (b) $P^2t^2/2m$
The impulse gives $p=Pt$, and $E_k=p^2/2m=P^2t^2/2m$.
5.An 8.0 kg box slides along a horizontal frictionless floor at $3\ \mathrm{m\,s^{-1}}$ and meets a light spring that compresses 12 cm before the box stops. Calculate the retarding force of the spring. (MDCAT 2023)
Correct answer: (c) 300 N
$\tfrac{1}{2}mv^2=\tfrac{1}{2}(8)(3)^2=36$ J, and $F=W/d=36/0.12=300$ N.
6.Two bodies with kinetic energies in the ratio 4 : 1 are moving with equal linear momentum. The ratio of their masses is: (MDCAT 2023)
Correct answer: (a) 1 : 4
With $p$ equal, $E_k=p^2/2m$, so the kinetic energy is inversely proportional to the mass.
All 20 Energy and Kinetic Energy MCQs → Energy and Kinetic Energy notes →
7.A 3 kg stone falls from a 20 m high platform. Find its speed at a height of 10 m. (MDCAT 2020)
Correct answer: (b) $14\ \mathrm{m\,s^{-1}}$
It has fallen 10 m, so $v=\sqrt{2gh}=\sqrt{2(10)(10)}\approx14\ \mathrm{m\,s^{-1}}$.
8.A long spring, when stretched by a distance $x$, has potential energy $V$. On increasing the stretching to $nx$, the potential energy of the spring will be: (MDCAT 2022)
Correct answer: (c) $n^2V$
$E=\tfrac{1}{2}kx^2$ goes as the square of the extension.
9.Ignoring friction and the extra forces exerted by the muscles, a pole vault is the conversion of an athlete's running kinetic energy into gravitational potential energy. If an athlete is to lift his body 5 m during a vault, what speed must he have when he plants his pole? (MDCAT 2022)
Correct answer: (b) $10\ \mathrm{m\,s^{-1}}$
$\tfrac{1}{2}mv^2=mgh$ gives $v=\sqrt{2gh}=\sqrt{2(10)(5)}=10\ \mathrm{m\,s^{-1}}$.
All 19 Potential Energy and Absolute Potential Energy MCQs → Potential Energy and Absolute Potential Energy notes →
10.The kilowatt-hour is a unit of: (MDCAT 2020)
Correct answer: (a) electric energy
It is a power multiplied by a time, so it measures energy.
11.One kilowatt-hour is equal to: (MDCAT 2020)
Correct answer: (b) $3.6\times10^{6}\ \mathrm{J}$
$1000\ \mathrm{W}\times3600\ \mathrm{s}=3.6\times10^{6}$ J.
12.The consumption of energy by a 60 W bulb in 2 s is: (MDCAT 2022)
Correct answer: (a) 120 J
$E=Pt=60\times2=120$ J.
All 30 Power MCQs → Power notes →
13.Which of the following is a non-conservative force? (MDCAT 2024)
Correct answer: (a) frictional force
The work done against friction depends on the path taken and is not recovered, so friction is non-conservative.
14.In inter-conversion of energy, the work done against the friction is: (SZABMU MDCAT 2023)
Correct answer: (c) fh
Work is force times distance, so the work against a friction $f$ over a distance $h$ is $fh$.
15.A bullet of mass 10 g leaves a rifle at an initial velocity of 1000 m/s and strikes earth at the same level with a velocity of 500 m/s. The work done in overcoming the resistance of air will be: (PMC Practice 2021)
Correct answer: (c) 3750 J
$\tfrac12\times0.01\times(1000^2-500^2)$ is $3750\,\mathrm{J}$ lost to the air.
Work Done Against Friction in a Resistive Medium notes →
16.An engine pumps 400 kg of water through a height of 10 m in 40 s. Find the power of the engine if its efficiency is 80%? Take g = 10msJ\-2. (PMC MDCAT 2022)
Correct answer: (c) 1.25 kW
The useful power is $400\times10\times10/40=1000\,\mathrm{W}$, and at $80\%$ efficiency the engine must supply $1.25\,\mathrm{kW}$.