ES2B00
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SECTION B : DYNAMICS
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3.
(a)
i. Briefly describe the difference between conservative and non-conservative forces, giving
one example of each. (3 marks)
A block of mass 2.5 kg is projected down a frictionless slope with an initial speed of 10 ms-1,
from a distance H above ground level (see Fig. 5). The speed of the block is 20 ms-1 when it
reaches ground level (at y = 0). Neglecting non-conservative forces, calculate:
ii. the kinetic energy of the block at ground level (at y=0) ; (2 marks)
iii. the work done by gravity on the block, in moving it from y=H to y=0 ; (3 marks)
iv. the potential energy of the block (relative to ground level) at y=H; (1 marks)
v. the initial distance above ground level, H. (2 marks)
Consider a similar problem to that depicted in Fig 5, but with a rough slope that
generates a frictional force on the moving block. In this case, the block is lighter (1 kg) and
has an initial speed of 5 ms-1 . During the descent from y=H to y=0 the frictional force
removes 150 J of energy from the system, resulting in a final speed at ground level of 10 ms-1.
Calculate:
vi. the initial distance above ground level, H. (3 marks)
Fig. 5
Question 3 Continued Overleaf
6
____________________________________________________________________
SECTION B : DYNAMICS
____________________________________________________________________
3.
(a)
i. Briefly describe the difference between conservative and non-conservative forces, giving
one example of each. (3 marks)
A block of mass 2.5 kg is projected down a frictionless slope with an initial speed of 10 ms-1,
from a distance H above ground level (see Fig. 5). The speed of the block is 20 ms-1 when it
reaches ground level (at y = 0). Neglecting non-conservative forces, calculate:
ii. the kinetic energy of the block at ground level (at y=0) ; (2 marks)
iii. the work done by gravity on the block, in moving it from y=H to y=0 ; (3 marks)
iv. the potential energy of the block (relative to ground level) at y=H; (1 marks)
v. the initial distance above ground level, H. (2 marks)
Consider a similar problem to that depicted in Fig 5, but with a rough slope that
generates a frictional force on the moving block. In this case, the block is lighter (1 kg) and
has an initial speed of 5 ms-1 . During the descent from y=H to y=0 the frictional force
removes 150 J of energy from the system, resulting in a final speed at ground level of 10 ms-1.
Calculate:
vi. the initial distance above ground level, H. (3 marks)
Fig. 5
Question 3 Continued Overleaf
6
