Physics- check answer please

1. A 15 kg boy falls out of his bed at a height of 0.50 m. What is the amount of gravitational potential energy lost by the boy?

my answer: 74 J

2. What is the speed of a 0.25 kg ball if its kinetic energy is 15 J?

my answer: 11 m/s

3. if the speed of an object is tripled and the mass is halved by what factor does the kinetic energy change?

my answer: 9/2

4. a ball is thrown up in the air. Which of the following quantities increases as the ball gets higher?

my answer: gravitational potential energy

5. a 10.0 kg crate slides across the floor 13 m against a force of friction of 7.5 N. what is the thermal energy produced?

my answer: 98 J

6. in the process of being thrown, a 500.0 g ball goes from rest to a speed of 10.0 m/s over a distance of 0.75 m. What is the force that was exerted on the ball?

my answer 33N

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  1. 1. PE = mg*h = 15 *9.8*0.5 = 73.5 J.

    2. 0.5*0.25*V^2 = 15
    0.125V^2 = 15
    V^2 = 120
    V = 11 m/s.

    3. KE1 = 0.5m*V^2
    KE2 = 0.5*(0.5m)*(3V)^2 = 0.5*0.5m*9V^2 = 0.25m*9V^2 = 2.25m*V^2.

    KE2/KE1 = 2.25m*V^2/0.5m*V^2=4.5 = 9/2.

    4. You didn't show the choices. However,
    PE = mg*h. Therefore. PE increases with
    height.

    6. a = (V^2-Vo^2)/2d = (10^2-0)/1.5 =
    66.67 m/s^2.

    F = m*a = 0.5 * 66.67 = 33.33 N.

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