Answer: h = 0.30 m
Explanation:
A person jumping from height h would possess potential energy = m g h
which will convert completely into kinetic energy as person hits the ground. Now, the maximum energy absorbed by the person can be = 200 J
m = 67 kg
g = 9.8 m/s²
⇒ m g h = 200 J
⇒ h = 200 J / (67 kg × 9.8 m/s²) = 0.30 m
Hence, a person can land safely on both legs without breaking them from a height of 0.30 m only.
a) Let's call x the direction parallel to the river and y the direction perpendicular to the river.
Dave's velocity of 4.0 m/s corresponds to the velocity along y (across the river), while 6.0 m/s corresponds to the velocity of the boat along x. Therefore, the drection of Dave's boat is given by:

relative to the direction of the river.
b) The distance Dave has to travel it S=360 m, along the y direction. Since the velocity along y is constant (4.0 m/s), this is a uniform motion, so the time taken to cross the river is given by

c) The boat takes 90 s in total to cross the river. The displacement along the y-direction, during this time, is 360 m. The displacement along the x-direction is

so, Dave's landing point is 540 m downstream.
d) If there were no current, Dave would still take 90 seconds to cross the river, because its velocity on the y-axis (4.0 m/s) does not change, so the problem would be solved exactly as done at point b).
Answer:
-929.5Joules
Explanation:
To get the work done by sam, we will calculate the kinetic energy of sam expressed as;
KE = 1/2mv²
m is the mass = 1100kg
v is the velocity = 1.3m/s
KE = 1/2(1100)(1.3)²
KE = 550(1.69)
KE = 929.5Joules
Since Sam is opposing the direction of movement, work done by him will be a negative work i.e -929.5Joules
True
It goes triassic, Jurassic, Cretaceous