First slide

Concept of potential energy

Question

The system shown in figure is released from rest. String is massless and pulley is smooth. The loss of potential energy of 4kg block in 3 seconds is

Difficult

A

590J
B

1080J
C

1200J
D

1400J

Solution

$\begin{array}{l} ΔU = m g Δ h \\ ΔU = 4 g \frac{1}{2} a t^{2} \\ ΔU = 4 \times 10 \times \frac{1}{2} \frac{(4 - 1) 10}{5} \times 9 \\ ΔU = 40 \times \frac{1}{2} \times \frac{3 \times 10}{5} \times 9 \\ ΔU = 1080 J \end{array} (∵ a = \frac{(m_{2} - m_{1}) g}{m_{2} + m_{1}})$

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