Forces, Movement, Shape, and Momentum
4 marks · EasyA student pushes a wooden block of mass 0.5 kg along a table. There is a force due to friction acting between the block and the table. The block is attached to a spring and a ruler is used to measure the extension of the spring as it moves.
State one effect of friction on the motion of the block.
The table below shows the force measured by the spring and the extension of the spring for different trials.
| Force (N) | Extension (cm) |
|---|---|
| 0.0 | 0.0 |
| 1.0 | 1.4 |
| 2.0 | 2.8 |
| 3.0 | 4.2 |
State whether this spring obeys Hooke’s law in these trials. Give a reason for your answer.
Describe what will happen to the extension of the spring if a larger force is applied and the spring is stretched beyond its elastic limit.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Friction slows the block down or opposes its motion.
(b) Yes, the spring obeys Hooke’s law because extension increases in equal steps for equal increases in force (linear relationship).
(c) The extension will increase more than expected and the spring will not return to its original length.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States friction slows the block down or opposes its motion.
B1 (b) · 1 mark · States spring obeys Hooke’s law (from the data given).
B1 (b) · 1 mark · Gives a reason: extension is proportional to force / relationship is linear.
B1 (c) · 1 mark · Describes that spring does not return to original length / extension increases faster / beyond elastic limit.
Worked solution
(a) Friction acts to slow down the block or oppose its movement along the table.
(b) The extension increases by 1.4 cm for every 1 N increase in force. This shows a linear relationship: extension is proportional to force. Therefore, the spring does obey Hooke’s law in these trials.
(c) If the spring is stretched beyond its elastic limit, the extension will increase more than expected and the spring will not return to its original length after the force is removed.