Help: HSC Success One Physics Q (1 Viewer)

[sunjet]

As the title says.
Space: Short Answers can anyone do question 3. b and 4. b. It's projectile motion so do it physics way please(ie. with motion formula's) not 3U way.

Thanks in advance.

 

[rama_v]

Vertical = U_y is U Sin15
Horizontal is U_x Cos15

Max height occurs when Usin15 = 0 (i.e. when vertical velocity = 0 )
0 = USin15 + (-9.8)t
9.8t = USin15

You also know that range is 7 m
X = U_xt
7 = U_xt
.: t = 7/U_x
This is the total time of flight. Max height occurs at half of the total time of flight, i.e. when t = 7/2U_x = 7/2Cos15

Sub this value of t back into 9.8t = USin15
so 9.8(7/2UCos15) = USin15
68.6 = 2U²Sin15Cos15
.: U = 11.7 ms^-1 to two decimal places

Notice how this is the way that the range formula is proved, because sin2@ = 2Sin@cos@ (as above)..

 

[sunjet]

thanks chief