Term 3 Block test :
Question 1:
Vector subtraction can be done using a drawing and calculation of the triangle obtained using sine and cosine rule. It has nothing to do with numerical subtration.
Vector subtration using component method can be done without any diagram. Subtract the x ccomp and then subtract the y comp and finally add the result using pythagoras theorem and tan of angle.
Try both methods !
Question 2:
For each part of the question , state cleary the start and end clearly.
i) start throwing does not mean velocity is zero. At time 2 s the stone is on the ground , which is 1.8 m below where it is thrown , hence s = -1.8m.
ii) start throwing but end at the highest point where the velocity is zero. The displacement is from the point thrown which is 1.8m above the ground.
iii) same start and end as part ii)
iv) start and end on the ground means the time taken is 2 s is used here.
b) If you choose up as positive , then the gradient is negative . It is not wrong to choose the other way round. Where the line cut the x axis is where it reaches the highest point and velocity is zero. It changes to negative direction and ends with a higher negative velocity as it hits the ground .
Question 3.
For part a i) and ii) , the net force is zero as the masses are at rest. When the string is cut the load free falls with g and the slider remain at rest. The weight component is not large at 6.7 N as compared to the friction of 17.8N . When the string is cut off the friction force will act opp to weight component and will be 6.7 N hence the slider is at rest.
Question 4
Forces must be drawn correctly . W and Rx and Ry at the base of ladder. Take moment about O at the base of the ladder.
W(2) = N (6)
N = 19.6 N
Rx = N , Ry = W
Hence R can be found using pythagoras theorem and tan angle
Answer: Rx= 19.6 N and Ry = 58.9 N
R= 62 N and angle = 71.6 north of east.
Question 5
b) The work done by friction = change in kinetic energy
work done = f x d
f = 24N
ii) Since B to C is smooth, no KE is lost , so the final EPE = KE at B. Hence x = 1.6 m
ci) The EPE is converted to KE . It is converted from KE to GPE and Heat before it finally come to a rest at the top of the slope.
ii) EPE = GPE + WD(by friction)
Ans = 0.96 m
