Answer:
Average recoil force experienced by machine will be 200 N
Explanation:
We have give mass of each bullet m = 50 gram = 0.05 kg
There are 4 bullets
So mass of 4 bullets = 4×0.05 = 0.2 kg
Initial speed of the bullet u = 0 m/sec
And final speed of the bullet v = 1000 m/sec
So change in momentum 
Time is given per second so t = 1 sec
We know that force is equal to rate of change of momentum
So force will be equal to 
So average recoil force experienced by machine will be 200 N
As per FBD while its accelerating upwards
we can say that

here normal force is given as


now mass is given as


now we will have


Now while accelerating downwards we can say by FBD

again plug in all values


Answer:
Explanation:
Comment
You could calculate it out by assuming the same starting temperature for each substance. (You have to assume that the substances do start at the same temperature anyway).
That's like shooting 12 with 2 dice. It can be done, but aiming for a more common number is a better idea.
Same with this question.
You should just develop a rule. The rule will look like this
The greater the heat capacity the (higher or lower) the change in temperature.
The greater the heat capacity the lower the change in temperature
That's not your question. You want to know which substance will have the greatest temperature change given their heat capacities.
Answer
lead. It has the smallest heat capacity and therefore it's temperature change will be the greatest.
Answer:
Time taken to reach the tree
they have given the maximum height which is 25m
therefore...
v=u+at (upward)
0 = 45sin(20)-9.81t
t = 1.56s