# PHYSICS! PLEASE!

posted by
**Kim**
.

The following data concerns a tennis ball at a given instant before it is struck by a tennis racket;

horizontal momentum of tennis ball= 2.4Ns

kinetic energy of ball= 45J

a) why is correct to give the direction of the momentum but not the kinetic energy

b) write down in terms of the mass m and the velocity v of the body, expressions for

i) momentum

ii) the kinetic energy

c) use your answer to (b) to help calculate the mass and the velocity of the ball

d) when the racket hits the ball it strikes it with a constant force of 60N in a direction opposite to its momentum, ringing to rest momentarily

calulate

i)the time the tennis ball takes to stop

ii) the distance the tennis ball travels while stopping

e) the force of 60N then contiues to act on the tennis ball for a further 0.60s. calculate

i) the momentum of the ball

ii)the distance the tennis ball travels while stopping

a) Think on vectors and scalars.

b)mv, 1/2 mv^2

c) 1/2 mv^2= 45j mv= 2.4Ns

solve for m, and v.

d) Impulse= change of momentum

Force(deltatime)=m(Vi- vf) where vf is

then force*distance= KE lost.

e. Force*time=change in momentum, from mv=0 to mv= final

ii makes no sense, the ball went from stop to some final velocity.

i don't get part C

solving for mv