Projectile - Help Please?

Question

t t = 0, an object is projected with a speed v0 = 35 m/s at an angle q0 = 20° above the horizontal.The axes on the diagram show the x and y directions that are to be considered positive.

For parts a-g, calculate the requested quantities at t = 7 s into the flight:
a) The vertical acceleration of the object:

ay = m/s2 *
-9.8 OK
b) Its horizontal acceleration:

ax = m/s2 *
0 OK
c) Its vertical velocity:

vy = m/s
d) Its horizontal velocity:

vx = m/s
e) The angle to the horizontal at which the object is traveling (an angle above the horizontal should be reported as a positive number; an angle below the horizontal should be reported as a negative number). Please give your answer in degrees.

angle = °
f) Its vertical displacement, from where it started:

y = m
g) Its horizontal displacement, from where it started:

x = m
h) At what time does the object reach its maximum height?

tymax = s

Answer 1

Oh well -- two out of eight isn't bad. I recommend that you brush up on your kinematics equations.

> c) Its vertical velocity:

Its vertical velocity is changing by 9.8m/s every second, right?

So:
vy = v0y - (7s)g

v0y (initial vertical velocity) is, of course, v0(sin20).

> d) Its horizontal velocity:
Horizontal velocity stays the same throughout the flight. So vx at 7 seconds is the same as v0x. (Which of course is v0(cos20).)

> e) The angle to the horizontal
tanθ = vy/vx

> f) Its vertical displacement,
y = v0y(t) - gt²/2

> g) Its horizontal displacement...
x = v0x(t)

> h) At what time does the object reach its maximum height?
Same time at which vy has gone to zero.
tymax = v0y / g