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CHECK YOURSELF ANSWERS
1Let d be the distance between A and B and t1, t2 the travel times back and forth. Then d = 15 t1 = 30 t2, i.e. t1 = 2 t2. The average speed is then vÂ¯=2dt1+t2=2Ã30t23t2=20Â m sâ1
2Positive for 1.0 s on, because curve is concave up, negative for 0 s to 1.0 s and zero at 1.0 s.
3It takes 2 s to get to the maximum height and 2 to return so the required time is 4 s.
4aZero at about 0.4 s and 1.6 s.
bNegative from 0.4 s to 1.6 s.
cMost negative at 1.0 s.
dThe displacement from 0 s to 1.0 s is about the same in magnitude as that from 1.0 s to 2.0 s so the displacement at 2.3 s will be positive.
5K=12mu2. At the highest point, KE=12mu2 cos260Â°=12mu2Ã14=K4.
6Both H and R are inversely proportional to the acceleration of free fall and so both are halved.
