Free Fall
1. A dropped object in free fall (a) falls 9.8 m each second, (b) falls 9.8 m during the first second, (c)
has an increase in speed of 9.8 m/s each second, (d) has an increase in acceleration of 9.8 m/s
each second.
(c)
2. An object dropped from the top of a cliff takes 1.80 s to hit the water in the lake below. What is
the cliff’s height above the water?
15.9 m
3. A spring-loaded gun shoots a 0.0050-kilogram bullet vertically upward with an initial velocity of
21 m/s. (a) What is the height of the bullet 3.0 s after firing? (b) At what times is the bullet 12 m
above the muzzle of the gun?
(a) 19 m
(b) tup = 0.68 s; tdown = 3.6 s
4. (a) The World Trade Center and the Empire State Building in New York City have heights of
about 417 m and 381 m, respectively. If objects were dropped from the top of each, what would
be the difference in time in their reaching the ground? (b) What would be the time of fall for
Chicago’s Sears Tower, at 443 m?
(a) ∆t = 0.407 s
(b) 9.51 s
5. A superball is dropped from a height of 4.00 m. Assuming the ball rebounds with 95% of its
impact speed, how high will the ball go? (Would it be 95.0% of the initial height?)
3.61 m (no)
6. A photographer in a helicopter ascending vertically at a constant rate of 12.5 m/s accidentally
drops a camera out the window when the helicopter is 60.0 m above the ground. (a) How long
will it take the camera to reach the ground? (b) What will its speed be when it hits?
(a) 5.00 s
(b) 36.5 m/s
7. It takes 0.210 s for a dropped object to pass a window that is 1.35 m tall. From what height
above the top of the window was the object released?
1.49 m above the top of the window