Question

NI. A stone is thrown vertically upward with a st of 125m from the edee of a dla 750m high thig 2- 49 (a) How much later does it reach the bottom of the clhff? (b) What is its speed just hefore hitting (c) What total distance did it travel? -75m FIGURE 2-49 Problem N 2-7 Freely Falling Objects Neglect air resistance . (1) A stone is dropped from the top of a chEl It is seen to hit 49. (1) If a car rolls gcntly in 0) off a vertical cliff, how long 50. (h Estimate (a) bow long it took King Kong to fall straigh: the ground helow after 3,75s How high is the clif? does ะ1 take itto reach 55 km/h? down from the top of the Empiee Stale Builkding (3s0 m high) and (b) his vclocity just befose "landing 51. (11) A baseball is hit almost straight up into the air wth a speed of about 20 m/s (a) How high does it go () long is it in the air? 2. 411) Suppose you adjust your parden hose nozzle for a hard stream of water. You point the nozzie vertically spw ard at a height of 1.5 m above the ground thg. 2-4S). When you quickly turn off the norzls, you beat the water striking the ground nest to yoa for another 20s What is the water speed as it leaves the nozzle? FIGURE 2-45 Problem 62

Answer 1

81.

(a)

$t_1=\frac {2\cdot 12.5 }{9.8}\: s= 2.55\: s$

$75=12.5t+\frac {1}{2}\cdot 9.8 t^2$

$4.9t^2+12.5t-75=0$

$t=2.84\: s$

$T=t_1+t=5.39\: s$

(b)

$v=12.5+9.8\cdot 2.84=40.3\: m/s$

(c)

$d=\frac {2\cdot 12.5^2}{2\cdot 9.8}\: m= 15.94\: m$

$D=d+75=90.94\: m$

48.

$h=\frac {1}{2}gt^2=\frac {1}{2}\cdot 9.8\cdot 3.75^2=68.9\: m$

49.

$t=\frac {v}{g}=\frac {55\cdot 1000}{3600\cdot 9.8}\: s= 1.56\: s$

50.

(a)

$t=\sqrt { \frac {2h}{g}}=\sqrt {\frac {2\cdot 380}{9.8}}\: s= 8.80\: s$

(b)

$v=\sqrt {2\cdot 9.8\cdot 380}\: m/s=86.30\: m/s$

51.

(a)

$h=\frac {v^2}{2g}=\frac {20^2}{2\cdot 9.8}\: m= 20.4\: m$

(b)

$t=\frac {v}{g}=\frac {20}{9.8}\: s=2.04\: s$