Answer:
(a) 
(b) 
Explanation:
We can derive the initial speed of the rock from the equation of the speed in function of the time:
Using the given values for the speed at time t=1.7s, we get:
In words, the speed of the rock at launch is 34m/s (a).
Next, we use this to calculate the speed at t=4.9s:
This means that the speed of the rock at 4.9s after the launch is 14m/s (b), and the negative sign means that it is moving downwards.
We can calculate the length of each spring by using the relationship:
where
F is the force applied to the spring
k is the spring constant
x is the length of the spring (measured with respect to its rest position)
Re-arranging the equation, we have
The force applied to both spring is F=60 N. Spring A has spring constant of k=4 N/m, therefore its length with respect to its rest position is
Spring B has spring constant of k=5 N/m, so its length with respect to its rest position is
Therefore, the correct answer is
<span>
D.Spring A is 3 m longer than spring B because 15 – 12 = 3.</span>
Wearing rubber or stay away from water or/ and a conductor
Double displacement: parts of compounds switch places to form two new compounds
FYI
decomposition: a complex substance breaks down into two or more simple substances
Single displacement: a single substance replaces another substance in a compound
<span>Synthesis: two simple substances combine to form a new complex substance</span>
