RECTILINEAR MOTION
137
17.33
17.34
17.35
An object is dropped from a height 25 ft above the ground. At the same time another object is thrown straight
down from a height 50 ft above the ground. Both objects hit the ground at the same time. Find the initial
velocity of the second object.
I For the first object, s = 25 - I6t
2 . When s = 0, t = f. For the second object, 5 = 50 + v n t - 16t
2 .
Since the second object also hits the ground after f seconds,
If the position s of an object moving on a straight line is given by
show that its velocity is positive,
and its acceleration is negative and proportional to the cube of the velocity.
The velocity
and the acceleration
An object moves along the jt-axis so that its ^-coordinate obeys the law x = 3f
3 + 8t + 1. Find the time(s) when
its velocity and acceleration are equal.
Setting v = a, 9t
2 + 8 = 18t, 9t
2 - 18t + 8 = 0, (3f-2)(3f-4) = 0,
v = D,x = 9t
2 + 8. a = D,v = I8t.
137
17.33
17.34
17.35
An object is dropped from a height 25 ft above the ground. At the same time another object is thrown straight
down from a height 50 ft above the ground. Both objects hit the ground at the same time. Find the initial
velocity of the second object.
I For the first object, s = 25 - I6t
2 . When s = 0, t = f. For the second object, 5 = 50 + v n t - 16t
2 .
Since the second object also hits the ground after f seconds,
If the position s of an object moving on a straight line is given by
show that its velocity is positive,
and its acceleration is negative and proportional to the cube of the velocity.
The velocity
and the acceleration
An object moves along the jt-axis so that its ^-coordinate obeys the law x = 3f
3 + 8t + 1. Find the time(s) when
its velocity and acceleration are equal.
Setting v = a, 9t
2 + 8 = 18t, 9t
2 - 18t + 8 = 0, (3f-2)(3f-4) = 0,
v = D,x = 9t
2 + 8. a = D,v = I8t.