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Question:

A small block is connected to one end of a massless spring of unstretched length 4.9 m. The other end of the spring (see the figure) is fixed. The system lies on a horizontal frictionless surface. The block is stretched by 0.2 m and released from rest at t=0. It then executes simple harmonic motion with angular frequency ω=3π rad/s. Simultaneously at t=0, a small pebble is projected with speed v from point P at an angle of 45° as shown in the figure. Point P is at a horizontal distance of 10 m from O. If the pebble hits the block at t = 1 s, the value of v is (take g=10 m/s²)

√50m/s

√51m/s

√52m/s

√53m/s

Solution:

Time is given by t = 2v sinθ / g
1 = 2v sin45° / 10
v = √50 m/s