Question

A force of 2i+j-k Newtons acts on a body which is in rest. If the velocity of the body at the end of 20 seconds is 4i+2j-2k, the mass of the body is .................. .

Answer 1

force applied = 2 i + J - K Newtons
force applied for a time = 20 seconds
after 20 seconds The velocity becomes = 4 + 2 j - 2 k

let mass of that body = m
according to second law of Newtonion motion.
force = change in momentum / time taken
2 i + J - k = m x (4 i + 2 j - 2K) / 20
2 i + J - k = m x 2 (2 I + J - K) / 20
2 i + J - k = m x (2 i + J - k) / 10
(2 i + J - k) x 10 / (2 i + J - k) = m
10 = m

so the mass of the body is 10 kg.

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Answer 2

force applied = 2 i + J - K Newtonsforce applied for a time = 20 secondsafter 20 seconds The velocity becomes = 4 + 2 j - 2 k
let mass of that body = maccording to second law of Newtonion motion.force = change in momentum / time taken2 i + J - k = m x (4 i + 2 j - 2K) / 202 i + J - k = m x 2 (2 I + J - K) / 202 i + J - k = m x (2 i + J - k) / 10(2 i + J - k) x 10 / (2 i + J - k) = m10 = m
so the mass of the body is 10 kg.