Question

Question 5
(a) A train is moving at a velocity of 25 ms 1. It is brought to rest by applying the
brakes which produces a uniform retardation of 0.5 ms?. Calculate
(i) the velocity of the train after 10 s
(ii) If the mass of the train is 20000 kg then calculate the force required to
stop the train.


(b) (i) State the universal law of gravitation.
(ii) Express it in a mathematical form. (Explain the symbols used.)
(iii) State the value of universal gravitation constant in S.I. unit.​

Answer 1

Answer:

Question 5

a)

$u = 25m/s\\\\v= 0 m/s\\\\a = -0.5m/s^{2}$

By the first equation of motion,

$v = u + at$

Substituting the values,

$v = 25 + (-0.5)(10)\\\\v= 25- 5 = 20 m/s$

(i) The velocity of train after 10 s is 20 m/s

$m = 20,000 kg\\\\a=0.5m/s^{2}$

$F = ma$

Substituting,

$F = (20000)(0.5) = 10,000 N$

(ii) Force required to stop the train is 10,000 N

(b) (i) Universal law of gravitation states that - "Every particle in the universe attracts the other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them"

(ii) $F = G\frac{xy}{r^{2}}$ where G = universal gravitation constant, x = mass of the first body, y = mass of the second body, r = distance of separation between them

(iii) The value of the universal gravitational constant is $6.67X10^{-11} m^{3}kg^{-1}s^{-2}$

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