How Do You Calculate the Force Exerted by a Shopper on a Grocery Cart?

[crysland]

A shopper pushes a grocery cart 20.0 m at constant speed on level ground, against a 35.0 N frictional force. He pushes in a direction 25.0º below the horizontal.

Find the force the shopper exerts, using energy considerations.

I got stuck on this because they don't give the mass of the cart.

 

[haruspex]

How would you use the mass of the cart? Suppose it were given, what equations would you apply?
(I find it strange that they ask you to use energy considerations though.)

 

[crysland]

I need to find the x-component of the weight so I need to know the mass.

 

[haruspex]

I need to find the x-component of the weight so I need to know the mass.

What x component? Gravity acts vertically and this is a horizontal surface. It's the force applied by the pusher that is not horizontal.