4.1 The Position, Velocity, and
4.2 Two-Dimensional Motion with
4.3 Projectile Motion
4.4 Uniform Circular Motion
4.5 Tangential and
4.6 Relative Velocity and
Q4.2 No, you cannot determine the instantaneous velocity. Yes, you can determine the average velocity.
The points could be widely separated. In this case, you can only determine the average
velocity, which is
Q4.3 A parabola results, because the originally forward velocity component stays constant and the
rocket motor gives the spacecraft constant acceleration in a perpendicular direction.
Q4.4 (a) yes (b) no: the escaping jet exhaust exerts an extra force on the plane. (c) no (d) yes
(e) no: the stone is only a few times more dense than water, so friction is a signifi cant force on
the stone. The answer is (a) and (d).
Q4.5 The projectile is in free fall. Its vertical component of acceleration is the downward acceleration
of gravity. Its horizontal component of acceleration is zero.
Q4.6 (a) no (b) yes (c) yes (d) no. Answer: (b) and (c)
*Q4.7 The projectile on the moon is in fl ight for a time interval six times larger, with the same range of
vertical speeds and with the same constant horizontal speed as on Earth. Then (i) its range is (d)
six times larger and (ii) its maximum altitude is (d) six times larger. Apollo astronauts performed
the experiment with golf balls.