Which one of the following statements must be true if the expression x = v_o t +

Question

Which one of the following statements must be true if the expression x = v_o t + 1/2 st^2 to be used? A) x is constant. B) v is constant. C) t is constant. D) a is constant. E) Both v_o and t are constant. During a one-hour trip, a small boat travels 30.0 km north and then travels 40.0 km east. What is the boat's magnitude of average velocity for the one-hour trip? (a) 70 km/h b) 50 km/h (c) 30 km/h (d) 40 km/h (e) Not here A football is kicked at an angle theta with respect to the horizontal. Which one of the following statements best describes the acceleration of the football during this event if air resistance is neglected? A) The acceleration is zero m/s^2 at all times. B) The acceleration is 9.8 m/s^2 at all times. c) The acceleration is zero m/s^2 when the football has reached the highest point in its trajectory D) The acceleration is positive as the football rises, and it is negative as the football falls. E) The acceleration starts at 9.8 m/s^2 and drops to some constant lower value as the ball approaches the ground.

Explanation / Answer

8) This kinematic equation can only be used for uniformly accelerated motion i.e. 'a' is constant.

9) Total displacement of the boat, D = 30N + 40E

Average velocity, v = Total displacement / Total time taken

=> v = (30N + 40E) / 1 = 30N + 40E

Magnitude of average velocity, |v| = (302 + 402)1/2 = 50 km/h

10) If the air resistance is neglected, the only force acting on the football is gravity, so its acceleration is 9.8 m/s2 at all times.

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