Question

1) While a lawn mower moves forward 2 meters, a man pulls on the handle of the lawnmower with a force of 100 Newtons. The angle between the displacement of the lawn mower and the direction of the applied force is 135.6 degrees. How much work was done on the lawnmower by the man?

A) 200 Joules
B) - 200 Joules
C) zero
D) - 141 Joules
E) 141 Joules

2) If the lawn-mower had 300 Joules of kinetic energy before the man pulled on it, about how much kinetic energy does it have after the work done by the man? (Assume there are no energy losses to friction).

A) 440 Joules
B) 500 Joules
C) 300 Joules
D) negative kinetic energy
E) 160 Joules

3) A car changes its speed from 30 mph to 90 mph. How many times greater is its final kinetic energy compared to its initial kinetic energy?

A) eight times as much
B) four times as much
C) twice as much
D) three times as much
E) nine times as much

4) Assume that the car changes chemical potential energy (gasoline) into kinetic energy with the same efficiency at all speeds. How many times more gas will it take far the car to go from 30 to 90 mph, compared to going from zero to 30 mph?

A) twice as much
B) nine times as much
C) three times as much
D) six times as much
E) the same amount
F) eight times as much

5) The scalar product of two vectors is equal to ...(choose all correct responses).

A) the magnitude of the first vector times the magnitude of the second vector times the cosine of the angle between the vectors
B) the magnitude of one of the vectors multiplied by the component of the other vector that is parallel to the first vector
C) a vector quantity
D) the product of a scalar and a vector
E) none of the other answers is correct

Answer 1

1) Work is defined as the scalar product between the force and dispalcement

but, scalar product between to vectors is defined as

then the work is

if

2) according to work-energy theorem

if , then final kinetic energy is

3) if initial speed is , the initial kinetic energy is

and final speed is . then

5) option A

and option B