Answer:
Impulse: [tex]3\; {\rm kg\cdot m\cdot s^{-1}}[/tex] backwards.
Average force: [tex]300\; {\rm N}[/tex] backwards.
Step-by-step explanation:
The impulse on an object is the change in momentum. For an object of mass [tex]m[/tex], if velocity of the object changed from [tex]u[/tex] to [tex]v[/tex], the impulse on the object would be [tex](m)\, (v - u)[/tex].
Make sure all quantities are in standard units. Specifically, mass should be measured in kilograms:
[tex]m = 100\; {\rm g} = 0.1\; {\rm kg}[/tex].
Assume that the original direction of motion of the cricket ball is the positive direction. The initial velocity of this ball would be [tex]u = 10\; {\rm m\cdot s^{-1}}[/tex]. Since the ball turned back and travels in the opposite direction, the new velocity would be negative: [tex]v = (-20)\; {\rm m\cdot s^{-1}}[/tex].
The impulse on this object would be:
[tex]\begin{aligned} & (m)\, (v - u) \\ =\; & (0.1\; {\rm kg})\, ((-20)\; {\rm m\cdot s^{-1}} - 10\; {\rm m\cdot s^{-1}}) \\ =\; & (-3)\; {\rm kg \cdot m\cdot s^{-1}}\end{aligned}[/tex].
Note that the impulse is negative, meaning that the direction of the impulse would be backward- opposite to the initial direction of motion (the positive direction.)
Dividing the impulse on the object by the duration gives the average net force on the object:
[tex]\begin{aligned}& (\text{avg. net force}) \\ =\; & \frac{(\text{impulse})}{(\text{duration})} \\ =\; & \frac{(-3)\; {\rm kg\cdot m\cdot s^{-1}}}{0.01\; {\rm s}} \\ =\; & (-300)\; {\rm kg \cdot m\cdot s^{-2}} \\ =\; & (-300)\; {\rm N}\end{aligned}[/tex].
Again, the net force on the ball is negative because the direction of this force is opposite from the initial direction of motion.
Assuming that all other forces on this ball are negligible, the force that the bat exerted on the ball would be approximately equal to the net force on the ball: [tex]300\; {\rm N}[/tex] backwards.