A ball of 250g hits the floor at a velocity of 2,50 m/s at an angle of 70* relative to the vertical. The vertical force in function with time between the floor and the ball is:

Question

from 0 to 50 N : from 0 to 1 sec.
from 50 N to 100 N : from 1 to 2 sec.
constant 100 N : from 2 to 3 sec.
100 to 50 N : from 3 to 4 sec.
and 50 N to 0 N : from 4 to 5 sec.

What is the velocity of the ball after the collision if the ball bounces? Give the answer in terms of unit vectors and polar notation.

and just a theory question:

When I'm asked to find work done by air resistance against a skier on a slope, will I have to do:

Wr = -Fr*d

or is it affected by an angle:

Wr = -Fr*d*cosTHETA

I was thinking that it isn't because air resistance isn't a specific force acting at one spot but everywhere on the slope at the same time, unless it's what's acting on the skier himself, then I would have to add the angle into my calculations

Answer 1

First question:
The sum of the force*time products will tell you the total impulse in the vertical direction, from which the final vertical velocity can be calculated (by dividing by mass). It will tell you nothing about the impulse in the horizontal direction, which is not necessarily zero. The question is poorly conceived.

Second question:
(Air resistance force) * d, because that force will be opposite to the direction of motion, regardless of the hill angle.

Answer 2

thank you very much!

Answer 3

Actually the direction of the air rersistance force can be somewhat different from the direction opposite to motion, depending upon the body's inclination to the direction of motion. Ski jumpers take advantage of this by leaning forward and tilting their ski tips up to stay aloft longer.

Answer 4

but the angle will still have no effect right?