Some projectile questions. (1 Viewer)

[currysauce]

A horizontal drainpipe 6m above sea level empties stormwater into the sear, If the water comes out horizontally and reaches the sea 2m out from the pipe, find the initial velocity of th water, correct to 1.d.p. Let g = 10ms-² and neglect air resis.

answer is: 1.8m/s


2. Jack stands at the window of a building 6.2m about ground level. He throws his keys straight out the window (horizontally) and hopes that his friend Tom, who is standing 10.4m out from the base will catch them. Ignore air resis, and use g= 10, find the velocity at which Jack needs to throw his keys, to 1.d.p.

answer is : 9.3 m/s

 

[Pace_T]

A horizontal drainpipe 6m above sea level empties stormwater into the sear, If the water comes out horizontally and reaches the sea 2m out from the pipe, find the initial velocity of th water, correct to 1.d.p. Let g = 10ms-² and neglect air resis.

answer is: 1.8m/s

cartesian eqn:
y = (-gx^2)(1 + tanA)/2V^2 + xtanA

(this is in the maths in focus textbook if i remember correctly, so just get t the subject in x = vtcosA and sub in y = -gt^2/2 + vtsinA)

.'. when y = -6, x = 2

.'. - 6 = -5(4)(1)/v^2 + 2(0)
v^2 = 20/6
v = 1.82
= 1.8m/s

 

[Pace_T]

2. Jack stands at the window of a building 6.2m about ground level. He throws his keys straight out the window (horizontally) and hopes that his friend Tom, who is standing 10.4m out from the base will catch them. Ignore air resis, and use g= 10, find the velocity at which Jack needs to throw his keys, to 1.d.p.

answer is : 9.3 m/s

angle = 0degrees

cartesian eqn:
y = -gx^2(1 + TanA)/2v^2 + vtanA

g= 10, when y = -6.2, x = 10.4

.'. -6.2 = -10(10.4)^2(1 + 0)/2v^2 + v(0)
v^2 = -540.8/-6.2
v = 9.3m/s

 

[thunderdax]

is it possible to just use the way we learn in physics to answer these questions?

 

[acmilan]

They probably will expect you to derive the formulae

 

[lfc_reds2003]

Im sure the syllabus states that one cant use physics formulas and achieve full marks...