Physics Help PLEASE! Power, Energy, and Acceleration!

1) If a car accelerates uniformly from rest to 15 meters per second over a distance of 100 meters. the magnitude of the car's accleration is
a) 0.15 m/s c) 2.3 m/s
b) 1.1 m/s d) 6.7 m/s

I KNOW THE ANSWER IS "C" but how do you do it?

2) As a box is pushed 30 meters across a horizontal floor by a constant horizontal force of 25 Newtons, the kinetic energy of the box increases by 300 Joules. How much total internal energy is produced during the process?
a) 150 J c) 450 J
b) 250 J d) 750 J

I KNOW THE ANSWER IS "C". how do you do it?

3) What is the power output of an electric motor that lifts a 2kg block 15 meters vertically in 6 seconds?
a) 5J c) 49J
b) 5W d) 49W

THANK YOU SO MUCH!

Hey Sarah,

(1) Use this equation:

v^2=(v_0)^2+2a(x-x_0). Let's solve for a:

(15)^2=0^2+2a(100-0); a= 9/8 m/s^2, or (b)

(2) Use the work-energy relation: Change in work=Change in kinetic energy.

I'm a little confused though; according to this relation, shouldn't the amount of total internal energy produced during this process be 300 J?

(3) The definition of power is Joules per unit second. Gravitational potential energy is measured in units of Joules; it is mgh. So,

(2)(9.8)(15)/6= 49 W, so d)

Does this help?

David

Ggg