Physics, 01.08.2019 01:30 natie18

Aman of mass 80kg stands next to a stationary ball of mass 4kg on a frictionless surface. he kicks the ball forward along the surface with a speed 15m/s. calculate the man’s recoil speed.

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Answer from: murokh

We cause conservation of momentum. The initial momentum of the situation is zero, since momentum is given by p=mv. Initially v of the ball and man are zero so the total momenta (the sum of the ball's and man's momenta) is zero.
Conservation of momentum means the vector sum of the final momenta must equal zero. That is, they will be equal and opposite. When the ball goes forward at 15m/s the momentum is p=(4kg)x(15m/s)=60kgm/s.
The man must have the same momentum, but in the opposite direction (negative). We can find his speed by considering the magnitude of his velocity:
$m_{man}v_{man}=60 \frac{kgm}{s} \\ \\ (80kg)v_{man}=60 \frac{kgm}{s} \\ \\v_{man}= \frac{60 \frac{kgm}{s} }{80kg}=0.75 \frac{m}{s}$

Checking our work we see that an 80kg man moving at 0.75m/s gives
(80kg)(0.75m/s)=60kgm/s, as expected.

Answer from: Quest

The answer is a) taiga because taigas are cold

Answer from: Quest

force is based upon mass and acceleration.the statement is not always true.

it can be explained from newton's second law of motion.

as per newton's second law of motion the rate of change of momentum is directly proportional to the applied force and takes place along the direction of force.

mathematically it can be written as -

$f\alpha \frac{dp}{dt}$

⇒ $f= k \frac{dp}{dt}$

here k is the proportionality constant whose value is 1.

$f=\frac{dp}{dt}$

$f= \frac{d[mv]}{dt}$

$f= m\frac{dv}{dt} +v\frac{dm}{dt}$

$f=ma+v\frac{dm}{dt}$ [a is the acceleration=dv/dt]

hence we see that force not only depends on mass and acceleration but also on velocity and rate of change of mass. force f will depend on mass and acceleration only when mass is constant.

hence the statement that force is based upon mass and acceleration is false.

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