Question

s posltve and decreasing in magnitude. 12. A particle accelerates uniformly from a speed of 30 cm/s to 40 cm/s in 5 s and thereafter moves at a constant speed of 40 cm/s for an additional 3 s. The average speed over this total time interval is A. 35 cm/s. B. 27 cm/s. C. 0.45 cm/s. D. 37 cm/s. E. 73 cm/s. On a graph that shows position on the vertical axis and time on the horizontal axis, a parabolic curve that opens upward represents A. a motion with constant positive acceleration. B. a motion with constant negative acceleration. C. a motion with no acceleration. D. a m 13. otion with positive acceleration followed by a motion with negative acceleration E. a motion with negative acceleration followed by a motion with positive acceleration.

Answer 1

Q.12 The average speed over total time interval is calculated by, total distance traveled total time avg Consider 2 parts of motion: (a) Particle accelerates uniformly from 30 cm/s to 40 cm/s in 5s (b) Moves at constant speed 40 m/s for 3s Consider motion (a) The average velocity for motion a is given by, 30 + 40 cm cm 35-

And ta 5s Therefore distance travelled is given by, da ata (35) (5) cm -175 cnm Consider motion (b) vb - 40 cm/s Therefore distance travelled is given by, (40) (3) cm - 120 cm

From (1) da db avg ta t 175 120 cm 5+3 s 36.87 cm cm

Hence, option D is correct. Q.13 Time(t) The equation of given parabola in x and v coordinate is given b Where, c -constant

Therefore above equation in terms of displacement and time is written as We know, this equation represents motion with constant acceleration, where constant c is acceleration i.e s- at From graph, we can see, as time increases slope of the graph i.e. velocity is increasing, which implies positive acceleration. Therefore graph represents motion with constant positive acceleration. Option A