First slide

Conservation of mechanical energy

Question

A block of mass 1 kg slides down a curved track which forms one quadrant of a circle of radius 1m as shown in figure. The speed of block at the bottom of the track is v= 2 $m s^{- 1}$ . The work done by the force of friction is (g=10m/ $s^{2}$ )

Moderate

A

+4J
B

-4J
C

-8J
D

+8J

Solution

$W o r k d o n e b y f r i c t i o n = E_{f i n a l} - E_{i n i t i a l} = K E_{f i n a l} - P E_{i n i t i a l} K E = \frac{1}{2} \times m \times {(v)}^{2} = \frac{1}{2} \times 1 \times {(2)}^{2} P E = m g h = 1 \times 10 \times 1 W = \frac{1}{2} \times 1 \times {(2)}^{2} - 1 \times 10 \times 1 W o r k d o n e b y f r i c t i o n = - 8 J$

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