Physics II

Hello! I'm doing a physics practice test, and I have two questions I cannot seem to figure out. Any help would be appreciated.

1. If the magnitude of the sum of two vectors is less than the magnitude of either vector, then:
A. the scalar product of the vectors must be negative
B. the scalar product of the must be positive
C. the vectors must be parallel
D. the vectors must be anti-parallel
E. the vectors must be perpendicular

2. An airplane is flying north at 500 km/h. It makes a gradual 180° turn at constant speed, changing its direction of travel from north through east to south. The process 40s. The average acceleration of the plane for this in km/h·s is:
A. 12.5 km/h·s, north
B. 12.5 km/h·s, east
C. 12.5 km/h·s, south
D. 25 km/h·s, north
E. 25 km/h·s, south

1: pythagorean theorem kills E
draw 2 parallel vectors, and convince yourself that C is not possible
draw 2 antiparallel vectors, and convince yourself that D might be possible, so B is not
all that is left are A and D
draw vector pointing south, and a 2nd one pointing southwest (similar magnitude) -> counterexample to D
Answer is A

2:
Starting velocity +500 km/h
Ending velocity -500 km/h

Average acceleration = delta_v / delta_t

So, 1000 (km/h) / 40 (s) = 25 km/h/s

Clearly, if the plane is travelling north and ends up moving south, then the acceleration must be south.

whoops forgot the sahjay