IB Physics HL A.3 Work, energy and power questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

Type

Multiple choice Written

Difficulty

Easy Medium Hard

Question 1

Paper 2Medium13 marks

A $16\ \mathrm{kg}$ sled moves horizontally along a level track. A rope pulls the sled through a displacement of $6.0\ \mathrm{m}$ with a constant tension of $50\ \mathrm{N}$ at $35^\circ$ above the horizontal. A constant friction force of $18\ \mathrm{N}$ acts opposite to the motion. The sled’s initial speed is $1.0\ \mathrm{m\,s^{-1}}$ Ignore air resistance.

(a)

Calculate the work done on the sled by the tension in the rope.

[2]

(b)

Calculate the work done on the sled by friction.

[2]

(c)

Determine the work done by the resultant force on the sled over the displacement.

[2]

(d)

Determine the sled’s speed after it has moved through $6.0\ \mathrm{m}$

[3]

(e)

Account for the difference between the work done by the rope and the increase in the sled’s kinetic energy.

[2]

(f)

In a repeat run, the rope is at $50^\circ$ above the horizontal. The tension, displacement, initial speed and friction force are unchanged. Calculate the work done by the rope and deduce whether the sled’s final speed is greater or smaller than in the first run.

[2]

Question 2

Multiple choiceHard1 mark

An electric winch raises a 40 kg load 6.0 m up a ramp at constant speed. The rope exerts a constant 250 N force parallel to the load’s 12 m displacement. The winch receives 4.0 kJ of electrical energy. Take $g=10\ \mathrm{N\,kg^{-1}}$ and assume all energy not retained as gravitational potential energy is transferred to thermal stores.

I. The work done by the rope on the load is 3.0 kJ.
II. A Sankey diagram for the winch and load together shows 2.4 kJ of useful gravitational potential energy output and 1.6 kJ of thermal output.
III. The work done by the rope on the load equals the load’s increase in gravitational potential energy.

Which statements are correct?

Show answer and explanation

Answer: C. The rope’s work is $W=Fs=(250)(12)=3.0\times10^3\ \mathrm{J}$ so I is true. The increase in gravitational potential energy is $mg\Delta h=(40)(10)(6.0)=2.4\times10^3\ \mathrm{J}$ For the winch and load together, the remaining $4.0-2.4=1.6\ \mathrm{kJ}$ is transferred to thermal stores, so II is true; not all the rope’s work is retained as gravitational potential energy, making III false.

A: Uses the vertical rise rather than the displacement parallel to the rope force to evaluate the work in I.
B: Treats all $3.0\ \mathrm{kJ}$ of rope work as useful gravitational potential energy, leaving only $1.0\ \mathrm{kJ}$ as thermal output.
D: Equates the rope’s energy transfer with the energy retained as gravitational potential energy, overlooking the thermal transfer.

Remember: work is energy transferred by a force; it need not all be retained in one energy store.

The best questions are still waiting

Unlock every question in this topic, then type, photograph or draw your answer and have it marked against the markscheme. Find out where you are dropping marks.

Unlock all questions Compare Student and Student Plus