Physics 9702 · AS & A Level · Energy conservation

Energy conservation — practice question

(a(i))[1]

State what the term work done means.

(a(ii))[1]

State the meaning of elastic potential energy.

(b(i))[2]

A block with mass $0.40\,\text{kg}$ moves in a straight line at a steady speed of $0.30\,\text{m s}^{-1}$ across a horizontal surface, as shown in Fig. 3.1. The block collides with a spring and slows down. The block stops when the spring has been compressed by $8.0\,\text{cm}$. Calculate the block’s initial kinetic energy.

(b(ii))[3]

Fig. 3.2 shows how the spring’s compression $x$ varies with the force $F$ applied to it. Use your result from (b)(i) to find the largest force $F_{\text{MAX}}$ exerted on the spring by the block. Show your working.

(b(iii))[1]

Find the block’s maximum deceleration.

(b(iv))[2]

State and explain whether the block is in equilibrium (1) before it reaches the spring, (2) when its speed is zero.

(c)[2]

The energy $E$ stored in a spring is given by $E = \frac{1}{2}kx^2$, where $k$ is the spring constant of the spring and $x$ is its compression. The mass $m$ of the block in (b) is now changed. The initial speed of the block stays constant and the spring continues to obey Hooke’s law. On Fig. 3.3, sketch how the maximum compression $x_0$ of the spring varies with mass $m$.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: Work done is the product of the force and the distance moved in the force’s direction

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