Ncert Exercises & Solutions

4.8 Three girls skating on a circular ice ground of radius 200 m start from a point P on the edge of the ground and reach a point Q diametrically opposite to P following different paths as shown in Fig. 4.20. What is the magnitude of the displacement vector for each? For which girl is this equal to the actual length of path skate?

D i s p l a c e m e n t f o r e a c h g i r l = \vec{P Q}

|\vec{P Q}| = D i a m e t e r o f c i r c u l a r i c e g r o u n d

= 2 \times 200 = 400 m

I t i s v e r y a p p a r e n t f r o m t h e f i g u r e,

F o r g i r l B, t h e m a n i t u d e o f d i s p l a c e m e n t = l e n g t h o f p a t h s k a t e .

4.9 A cyclist starts from the center O of a circular park of radius 1 km, reaches the edge P of the park, then cycles along the circumference, and returns to the center along QO as shown in Fig. 4.21. If the round trip takes 10 min, what is the

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