Question 8
(a) A jet starts from rest with an acceleration of 3 ms-2 and makes a run for 30 s before taking off. Calculate the:
(i) distance travelled before the take-off.
(ii) velocity of the plane at takeoff.
(ii) Two bodies of masses 6 kg and 4 kg moving in opposite directions with velocities of 9 ms-1 and 7 ms-1 respectively, collide and move together. Calculation their common velocity.
(c) State:
(i) the Pascal’s principle;
(ii) Two application of the Pascal’s principle; (iii) the condition for a body to float in a liquid.
Observation
Part (a) Well attempted by most candidates.
Part (b) Many candidates attempted this question correctly.
Part (c) Candidates performance was average.
Part (d) Candidates performance was below average.
The expected answer is:
8. (a)
(i) Calculation of the distance travelled before take-off
s = ut + ½at2
= 0 + ½ 3 302
= 1350 m
(ii) Calculation of velocity of plane at take-off
v = u + at
= 0 + 3 30
= 90 m s-1
(b)
(i) Difference between elastic collision and inelastic collision
In elastic collision, both kinetic energy and momentum are conserved
while in inelastic collision, only momentum is conserved.
OR
In elastic collision, the colliding bodies separate after impact while
inelastic collision they stick together.
(ii) Calculation of common velocity of bodies
=m1u1 – m2u2 = (m1 +m2)v (1)
= (6 x 9) – (4 x 7) = (6 + 4)v (½)
= 54 – 28 = 10v (½)
= v = 2.6 m s-1 (1)
(c) (i) Pascal’s principle
The pressure applied at any point in an enclosed
fluid at rest is transmitted equally in all directions.
- Hydraulic press
- Car brake system
- Pressure gauges
- Syphons
It must displace its own weight of the fluid in which it floats.
OR
Its buoyant force/upthrust must balance its weight.