13. -2 points SerPSE9 7 P03 Ask Your A 7.80-g bullet moving at 540 m/s strikes t

Question

13. -2 points SerPSE9 7 P03 Ask Your A 7.80-g bullet moving at 540 m/s strikes the hand of a superhero, causing the hand to move 4.60 cm in the direction of the bullet's velocity before stopping. (a) Use work and energy considerations to find the average force that stops the bullet. (b) Assuming the force is constant, determine how much time elapses between the moment the bullet strikes the hand and the moment it stops moving. 14. -3 points Se PSES 7 P042 A 250-N child is in a swing that is attached to a pair of ropes 2.20 m long. Find the gravitational potential energy of the child-Earth system relative to the child's lowest position at the following times. (a) when the ropes are horizontal (b) when the ropes make a 32.0° angle with the vertical (c) when the child is at the bottom of the circular arc Need Help? WeehN 15 -2 points SerPSES 7 P047 so The potential energy of a system of two particles separated by a distance r is given by the equation below, where A is a positive constant. U (r) Find the radial force that each particle exerts on the other. (Use any variable or symbol stated above as necessary.) and is pointing Selefrom the other particle

Explanation / Answer

12)

Mass of the bullet, m = 7.8 g = 7.8 x 10^-3 Kg

Initial speed u = 540 m/s

Final speed v = 0

Distance covered s = 4.60 cm = 0.046 m

(a)

According to work energy theorem

Work done W = Change in Kinetic energy

F x S  = (1/2)mu^2

F x 0.046 = 1/2 x 7.8 x 10^-3 x (540)^2

F = 24722.6 N

b)

From Impulse definition

F x t = Change in momentum

24722.6 x t = 7.8 x 10^-3 x 540

t = 0.00017 sec or 0.17 ms

  

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