# AS Level maths mechanics question

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#1
"In this question use g=9.81. A small stone is projected vertically upwards from the top of a cliff, with speed ums^-1. It hits the ground with a speed of 18.2ms^-2. A second small stone is also projected vertically upwards with speed ums^-2 from a nearby cliff which is 4.5m higher. It takes 2.97s to hit the ground. Find the value of u and the height of the first cliff."

Ok so I'm absolutely clueless as to what to do here. I know that you have to use SUVAT, and that maybe there's a simultaneous equation involved but I'm very stuck. Can anyone help?
0
1 year ago
#2
with speed ums^-2? you mean u ms^-1. Maybe draw a sketch of the scenario and write SUVAT for each scenario, a SUVAT for the normal cliff and a SUVAT for the higher cliff. Then solve simultaneously. With this, you should get:

SUVAT for shorter cliff:

S = -H (I'm calling upwards positive, the net displacement travelled is -H, and H being the height of the cliff)
U = u (projection speed)
V = -18.2
A = -9.81
T = ? (you don't really need this)

SUVAT for higher cliff:

S = -4.5-H
U= u
V = ?? (don't need this
A = -9.81
T = 2.97

And solve simultaneously to find u and H
Last edited by { }; 1 year ago
1
#3
Ok, which SUVAT equation would you use? Because none of the equations contain the same given values.
(Original post by { })
with speed ums^-2? you mean u ms^-1. Maybe draw a sketch of the scenario and write SUVAT for each scenario, a SUVAT for the normal cliff and a SUVAT for the higher cliff. Then solve simultaneously. With this, you should get:

SUVAT for shorter cliff:

S = -H (I'm calling upwards positive, the net displacement travelled is -H, and H being the height of the cliff)
U = u (projection speed)
V = -18.2
A = -9.81
T = ? (you don't really need this)

SUVAT for higher cliff:

S = -4.5-H
U= u
V = ?? (don't need this
A = -9.81
T = 2.97

And solve simultaneously to find u and H
0
1 year ago
#4
Ok, which SUVAT equation would you use? Because none of the equations contain the same given values.
You need to use a different equation for each of the two scenarios.
1
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