Answer:
The answer is first one 1...
Answer:
a. 16 s b. -1.866 kJ
Explanation:
a. Since the initial rotational speed ω₀= 3313 rev/min = 3313/60 × 2π rad/s = 346.94 rad/s. Its rotational speed becomes ω₁ = 0.75ω₀ in time t = 4 s.
We find it rotational acceleration using α = (ω₁ - ω₀)/t = (0.75ω₀ - ω₀)/t = ω₀(0.75 - 1)/t = -0.25ω₀/t = (-0.25 × 346.94 rad/s)/4 s = -21.68 rad/s².
Since the turntable stops at ω = 0, the time it takes to stop is gotten from
ω = ω₀ + αt and t = (ω - ω₀)/α = (0 - 346.94 rad/s)/-21.68 rad/s² = (-346.94/-21.68) s = 16 s.
So it takes the turntable 16 s to stop.
b. The workdone by the turntable to stop W equals its rotational kinetic energy change.
So, W = 1/2Iω² - 1/2Iω₀² = 1/2 × 0.031 kgm² × 0² - 1/2 × 0.031 kgm² × (346.94 rad/s)² = 0 - 1865.7 J = -1865.7 J = -1.8657 kJ ≅ -1.866 kJ
Answer:E
Explanation:
It is given that Energy of gamma ray is E=1.2 Mev
Shielding effect can be measured by measuring the fraction of gamma rays blocked by shield. If certain thickness will able to block half the radiation then to block 75% radiation we need to add same amount of thickness in order to block the remaining radiation.
i.e.
fraction is blocked by 10 cm thickness
then remaining radiation is 
another 10 cm thickness will block the remaining half radiation i.e.
so total 75 % radiation will be blocked
Vertical line from the centre of mass is inside the base of the tower.
Answer:
3.24 m/s
Explanation:
Suppose that the boat sails with velocity (relative to water) direction being perpendicular to water stream. Had there been no water flow, it would have ended up 0m downstream
Therefore, the river speed is the one that push the boat 662 m downstream within 539 seconds. We can use this to calculate its magnitude

So the boat velocity vector relative to the bank is the sum of of the boat velocity vector relative to the water and the water velocity vector relative to the bank. Since these 2 component vectors are perpendicular to each other, the magnitude of the total vector can be calculated using Pythagorean formula:
m/s